Buffalo Bills head coach Chan Gailey, right, reaches out to running back Fred Jackson (22) as Jackson is helped off the field. (AP Photo/Bill Wippert)

ORCHARD PARK, N.Y. (AP) — The Buffalo Bills officially placed running back Fred Jackson on injured reserve Tuesday and promoted defensive tackle Jay Ross to the 53-man roster.

Jackson won’t require surgery after being diagnosed with a Grade 2 sprain to his MCL this week, but with the Bills at 5-8 and looking toward next season, the move became an obvious one.

“He’s not going to make it,” Buffalo coach Chan Gailey said Monday.

His injury leaves Buffalo with just two active running backs, C.J. Spiller and Tashard Choice. Gailey said fullback Corey McIntyre could fill the third spot if necessary, and on Tuesday, Buffalo also signed running back Zach Brown to the practice squad.

Ross spent portions of the past two seasons on Buffalo’s practice squad. A three-year starter at East Carolina, the 6-3, 319-pound lineman entered the NFL as an undrafted free agent with New Orleans in 2010.