Coach Chan Gailey provided the update on Monday saying Jackson is expected to miss between three and five weeks. And that won't be enough time to recover considering the Bills (5-8) have only three games left and have all but mathematically been eliminated from playoff contention.
"No, he's not going to make it," Gailey said, a day after Jackson was hurt in the fourth quarter of a 15-12 loss to St. Louis.
Jackson won't require surgery after being diagnosed with a Grade 2 sprain to his MCL. Though the plans haven't been finalized, Gailey said it's likely the player will be placed on the season-ending injured reserve list.
His injury leaves Buffalo with just two running backs, C.J. Spiller and Tashard Choice. Gailey said he's not sure whether to add a running back because fullback Corey McIntyre could fill the third spot if necessary.
The Bills are preparing to "host" Seattle (8-5) at Toronto on Sunday.
Jackson was hurt with about 5:30 left, when two Rams defenders sandwiched his right leg in making a tackle during a 2-yard run.
Jackson lay on the field for several minutes and was unable to put much weight on his right leg while being helped off to the sideline. With a towel draped over his head, Jackson was then carted off to the locker room as fans chanted "Freddie! Freddie!"
The injury is the latest setback for Jackson this year, and is to the same knee he sprained in a season-opening 48-28 loss at the New York Jets. Jackson missed the next two games. He also missed a 19-14 win over Miami on Nov. 15 after sustaining a concussion a week earlier.
Jackson, who's led the team in rushing in each of the previous three years, has 437 yards rushing this season - his fewest in five seasons. He has scored three touchdowns rushing, and also has 217 yards receiving and a touchdown.
Jackson, who signed a two-year, $9 million contract extension in May, still led the Bills with 934 yards rushing last year despite missing the final six games with a broken bone in his right leg.
The Bills have a capable player to lean on in co-starter Spiller, who has 944 yards rushing and five touchdowns. The 2010 first-round draft pick is averaging 6.55 yards per carry, which is the NFL's second-best total through 13 games since 1960 for a player with a minimum of 130 attempts. Jim Brown averaged 6.61 yards per carry for the Cleveland Browns in 1963.