5:16pm: Mack suffered a broken fibula, according to Adam Schefter and Pat McManamon of ESPN.com, who report that it figures to be a season-ending injury for the Browns center (Twitter link).
4:27pm: Given that Browns center Alex Mack was forced to leave today’s game on a cart after suffering a leg injury, it was fair to speculate that the injury was relatively serious. We now know a few more details on the situation, as Cleveland head coach Mike Pettine told reporters, including Nate Ulrich of the Akron Beacon-Journal (via Twitter), that the initial diagnosis on Mack was a broken leg, although Pettine had not confirmed that information. Ian Rapoport of NFL.com (Twitter link) reports that the injury was actually a broken ankle — either way, Mack figures to miss the rest of the 2014 season.
Mack, a first-round pick in 2009, has never missed a game in his six-year career. After the Browns placed the transition tag on the 28-year-old during the offseason, Mack signed an offer sheet with the Jaguars, which Cleveland then matched. Per the agreement, Mack is set to earn $10MM this season, and $8MM in 2015 — both amounts are guaranteed. He’s well worth the money, as Pro Football Focus (subscription required) has graded Mack as a top-10 center during each season he’s been in the league.
To compensate for the loss of Mack during today’s 31-10 win over the Steelers, the Browns moved right guard John Greco to center, while inserting backup offensive lineman Paul McQuistan at RG. It’s unclear if the Cleveland will use this alignment going forward. The only other reserve offensive lineman on the squad is second-year player Vinston Painter, who is more of a guard/tackle. The Browns also have Ryan Seymour and Karim Barton on their practice squad, but again, both are G/T types who have no experience at center.