Mack, in his sixth year in the league, broke his fibula in Cleveland's 31-10 victory over the Pittsburgh Steelers last Sunday. Mack went down on a rushing play during the second quarter, and was carted off afterwards with an air cast on the injured leg.
Coach Mike Pettine was initially optimistic about Mack's recovery, saying on Monday that if the injury was just a broken bone, Mack could take the field again in eight to 10 weeks.
However, according to Rosenthal, putting Mack on IR is a more drastic move that might mean there has been damage to ligaments. Mack, drafted in the first round of the 2009 draft, had not missed a snap prior to going down in Week 6.
The offensive line, supporting a run-focused offensive attack, has been central to Cleveland's success. John Greco is likely to take over at center, and Paul McQuistan will likely take over Greco's spot at guard.
Cleveland, 3-2 and third in the AFC North, will travel to Jacksonville this weekend to face the 0-6 Jaguars.
- Christopher Woody