The Browns placed Mack (leg) on injured reserve Friday.

Mack will miss the rest of the season after breaking his leg in Week 6. John Greco will take over as the starting center in Mack's place.

Mack suffered a broken fibula Sunday against the Steelers, the Cleveland Plain Dealer reports.

This represents a big blow to the Browns' offensive line, with the two-time Pro Bowler likely out for the season. After Mack was injured Sunday, John Greco replaced him at center, while Paul McQuistan took over at right guard.

Mack was carted off the field Sunday after suffering what appeared to be a lower leg injury, the Cleveland Plain Dealer reports.

The exact nature of Mack's injury has yet to be announced by the team, but he looks to have suffered something potentially serious. John Greco took over for Mack at center, with Paul McQuistan coming off the bench to replace Grego at right guard. Since there's no backup center listed on the teams' official depth chart, this is likely the offensive line combination that will be used if Mack has to miss extended time. Considered to be one of the better centers in the league, Mack's loss could potentially be damaging to Cleveland rushing attack.

Alex Mack told the Cleveland Plain Dealer "there's no bad blood" between him and the Browns for failing to get a deal done last season.

Mack denies reports he wanted out of Cleveland and says he was strictly looking to maximize his free-agent value. The Browns matched Mack's five-year, $42 million offer sheet from Jacksonville, keeping him under contract for at least the next two seasons. Mack is the highest paid center in the league with an average annual salary of $8.4 million. He can opt out of his deal after the 2015 season.

Browns matched C Alex Mack's five-year, $42 million offer sheet from the Jaguars, keeping Mack in Cleveland.

They needed all of 2 1/2 hours to match Jacksonville's offer. A top-ten center in each of the past three seasons per Pro Football Focus, 28-year-old Mack finished No. 4 in PFF's 2013 ratings, behind only Jason Kelce, Dominic Raiola, and John Sullivan. It's good news for Ben Tate, as Mack is a particularly effective run blocker. The Jags will go back to the drawing board on the interior line, where they need new starters at both center and right guard. Cleveland's offensive line as it stands reads LT Joe Thomas, LG Jason Pinkston, C Mack, RG John Greco, and RT Mitchell Schwartz. It's a very strong core, and GM Ray Farmer has ten picks in May's draft, including five selections in the top 85.

Jaguars signed transition-tagged C Alex Mack to a five-year, $42 million offer sheet.

As expected. The Browns now have five days to match the offer. It includes $26 million guaranteed, an opt-out clause after 2015, and a no-trade provision. The deal will pay Mack $10 million in 2014 and $8 million in each of the four seasons after. The $8.4 million annual average makes Mack the league's highest-paid center, just ahead of Ryan Kalil. The $26 million guaranteed is $7 million more than Kalil got from Carolina. Odds are the Browns will match and retain Mack.

NFL.com's Ian Rapoport reports the Browns are "really thinking over" matching Jacksonville's five-year, $42 million offer for transition-tagged C Alex Mack, and that the Jags "made it tough."

You cannot stop the Alex Mack news-cycle, you can only hope to contain it. It's been the belief all week that the Browns would match any offer, but we suppose they could be having second thoughts. Mack is guaranteed $18 million over the next two seasons, and can opt out after 2015. It would still be very surprising if the Browns let Mack walk.

NFL.com's Ian Rapoport reports transition-tagged C Alex Mack's five-year offer sheet with the Jaguars is worth $42 million, and includes a player option after the 2015 season.

The deal includes $18 million guaranteed over the first two seasons. The $8.4 million average annual value will make Mack the highest-paid center in the league. Mack can void the deal after 2015, and cannot be franchise tagged if he does so. However, if Mack opts not to hit the market, he'll be guaranteed $8 million for 2016. It's a creative clause, but hardly a roadblock to the Browns matching Jacksonville's offer. Mack is expected to officially sign on Friday. Cleveland is fully expected to match.

NFL.com's Ian Rapoport reports transition-tagged C Alex Mack will officially sign his five-year offer sheet with the Jaguars on Friday.

ESPN's Adam Schefter reported Wednesday that Mack would sign the agreement "by Friday." The offer is expected to be creatively structured, but the Browns are fully expected to match. They have the Jags beat on cap space, pure and simple. Cleveland will have five days to match once Mack signs.

A source tells ESPN's Adam Schefter that the Browns figure to match Jacksonville's five-year offer sheet to transition-tagged C Alex Mack "in no time at all."

The offer is designed to make it as difficult as possible for the Browns to match, and Mack reportedly prefers to flee for Jacksonville. But Cleveland has the most cap space in the entire league and is going to use it to retain one of the game's most consistently excellent centers. They'll worry about extensions for Joe Haden, Josh Gordon and Jordan Cameron down the line. Mack is going to cost the Browns at least $18 million fully guaranteed over the next two seasons, making him the game's highest-paid center.

FOX Sports' Mike Garafolo reports Alex Mack's five-year offer sheet with the Jaguars will make him the NFL's highest paid center.

Mack is going to be the highest paid center in football regardless of whether he's playing in Jacksonville or Cleveland. Specific terms still aren't in, but Carolina's Ryan Kalil is currently the NFL's richest pivot. In August of 2011, the Panthers gave Kalil a six-year, $49 million contract. That deal contained $28 million guaranteed, including an $18 million signing bonus.

CBS Sports' Jason La Canfora reports Browns transition-tagged C Alex Mack has already agreed to terms with the Jaguars on an offer sheet.

The actual offer sheet has not been "drawn up," but "will be shortly and then submitted," per La Canfora. It's expected to be for five years. We're hoping the full terms will be made public by Friday. The Browns will have the opportunity to match the offer sheet once it's finalized with the league. The Jaguars have been very fiscally careful under GM Dave Caldwell, but would likely have to blow Mack away to prevent Cleveland from matching the contract offer.

ESPN's Adam Schefter reports the Jaguars will sign transition-tagged C Alex Mack to a five-year offer sheet by Friday.

Per Schefter, Mack badly wants to play the five-year contract with the Jaguars and doesn't want to return to Cleveland. Mack's agent and the Jaguars will structure the deal in a way that will make it as difficult as possible for the Browns to match it, even though Cleveland has a boat load of cap space and a desire to retain arguably the game's best center. Once the deal is signed, the Browns will have five days to make a decision. Mack is 28 years old.

The Cleveland Plain Dealer confirms the Jaguars are "contemplating" making an offer to transition-tagged C Alex Mack, but that the Browns are likely to match.

"We remain optimistic that Alex Mack will be a Cleveland Brown for a long time,'' owner Jimmy Haslam said Tuesday. "We want him to be. I think we've made it very clear that he's the kind of person, the kind of player we want in our organization." No matter how creative the Jags get with their offer sheet, the Browns - who have more salary-cap space than any team in the league - should be able to match.

The Cleveland Plain Dealer reports "talks are still ongoing" between transition-tagged C Alex Mack and the Jaguars.

It's possible the sides are working on a structure that the Browns couldn't match, but Cleveland still has the salary-cap edge, with roughly $5 million more in space than Jacksonville. The Jags clearly have eyes for Mack, but he'll still most likely end up back in Cleveland. For what it's worth, Browns owner Jimmy Haslam told reporters on Tuesday that he's "optimistic" Mack will remain in Cleveland.

A league source tells Profootballtalk.com the Browns would match a three-year, $22 million offer sheet from the Jaguars to transition-tagged C Alex Mack "in a second."

This is all just hypothetical for now -- no offer has been extended -- but it's notable because the Florida Times Union reported Saturday the Jaguars would have to come up with an offer of three years and at least $22 million guaranteed in order to land Mack. The Browns have already locked in Mack at $10.039 million for 2014, which suggests they see him as a $10-plus million per-year player. The three-year, $22 million idea would pay him only $7.3 million annually.

Profootballtalk reports free agent C Alex Mack hasn't taken any visits and is generating no interest.

As Mike Florio points out, it might be best for Mack to sign the one-year, $10.039 million transition tender the Browns slapped him with before GM Ray Farmer rescinds the offer. The money around the league is starting to dry up one week into free agency, so the chances of Mack landing a deal he likes appear slim. He can earn the hefty salary in 2014 and hit the open market again next March.

NFL Network's Ian Rapoport reports four teams have shown "varying levels" of interest in free agent C Alex Mack.

RapSheet mentions the Ravens and Colts as two of the teams interested in the 28-year-old. They're waiting for the "frenzy to die down" before making a run at Mack, who was slapped with the transition tag by the Browns. Indianapolis needs a center after releasing Samson Satele, while Baltimore needs an upgrade on Gino Gradkowski. Mack is arguably the best center in the NFL.

NFL Network's Ian Rapoport reports the Ravens could "make a play" for free agent C Alex Mack if they strike out on free agent LT Eugene Monroe.

A center isn't really a "backup" plan to an elite pass-protecting left tackle like Monroe. Rapoport's colleague, Mike Silver, also mentions the Bucs as a possible landing spot for Mack. The Browns slapped Mack with the transition tag, which means they only have the right of first refusal. Cleveland wouldn't get any compensation if Mack signs elsewhere. Mack played for Bucs OC Jeff Tedford in college. The Ravens badly need to upgrade on C Gino Gradkowski.

Transition player C Alex Mack fully intends to test the open market.