Bills running back Fred Jackson is out indefinitely after tests Monday revealed no definitive diagnosis on a possible lateral collateral ligament injury to his right knee.

Jackson took a direct hit to the knee from Jets safety LaRon Landry. He'll likely have further tests next week and be listed as "out" for Sunday's home opener against the Kansas City Chiefs.

Wide receiver David Nelson (right knee) was initially diagnosed with a torn ACL and is likely out for the season.

C.J. Spiller was the bright spot for the Bills offense in the 41-21 loss to the Jets and is likely to remain in the featured back role for several weeks.

Spiller had a career-best 169 yards against the Jets. Last season, he took over for Jackson as the lead man in Week 11 when Jackson suffered a broken leg at Miami.

Jackson went down with a knee injury in the second quarter at New York Sunday. The team's leading rusher in 2011, Jackson had 934 yards, and third-leading receiver with 39 catches for 442 yards, but missed the final six games.

-- The Sports Xchange

SI Apps
We've Got Apps Too
Get expert analysis, unrivaled access, and the award-winning storytelling only SI can provide - from Peter King, Tom Verducci, Lee Jenkins, Seth Davis, and more - delivered straight to you, along with up-to-the-minute news and live scores.