Bills place WR David Nelson on IR

The Buffalo Bills placed receiver David Nelson on season-ending injured reserve Tuesday and signed a running back to help with their depth at the position as a result of Fred Jackson's knee injury, which will keep the team's starter out for at least three weeks.

Nelson tore a ligament in his right knee in the Bills' season-opening loss to the New York Jets. On Tuesday, the Bills signed running back Johnny White to take his place. The 5-foot-10, 202-pound White rushed for 38 yards on 12 carries last season for the Bills after being selected by Buffalo in the fifth round of the 2011 draft. He had been released by the team on Aug. 31.

The Bills had already been thin at the running back position before Jackson's injury, with Tashard Choice serving as the lone running back behind Jackson and C.J. Spiller. The Bills do have two fullbacks in Corey McIntyre, who has mostly been used as a blocker, and Dorin Dickerson, who is expected to be used in the passing game.

Bills coach Chan Gailey announced the injuries suffered by Nelson and Jackson in his news conference Monday.

"It's a setback," Gailey said. "You lose experience and you lose versatility. But I think our guys can adjust."

Gailey described Jackson's injury as a sprained knee, and said he expects him to miss between three and seven weeks. A league source told ESPN NFL Insider Adam Schefter that an MRI conducted on Jackson's knee Monday was inconclusive, and added that doctors will re-evaluate the injury within the next 10 days.

Jackson told Bills fans via his Twitter page that he'll be back on the field as soon as possible.

He wrote: "Thanks for all the prayers all well wishes. I will get back on field ASAP! Keep Billieving in us, jus more work to do!!"

The injuries hit two key players on an offense that's already off to an inconsistent start after producing four turnovers against the Jets, including three interceptions by starter Ryan Fitzpatrick.

Buffalo will attempt to regroup when it faces the Kansas City Chiefs (0-1) in its home opener Sunday.

Nelson has been a reliable target in the slot, and finished second on the team with 61 catches for 658 yards and five touchdowns last season.

Jackson is a respected team leader who's been the Bills' dual-threat workhorse in both the running and receiving game. Despite missing the final six games with a broken bone in his right leg last year, Jackson still finished with 1,376 combined yards rushing and receiving to account for nearly a quarter of the Bills' total offense.

"It's a huge blow," running back Spiller said Monday. "But we can't sit around and mope and not regain focus. This just means somebody on offense has got to step up."

Spiller will take over for Jackson, much like he did last year after Jackson was hurt. Spiller did a solid job of filling in against the Jets in a game he finished with a career-best 169 yards rushing, including a 56-yard touchdown.

Nelson's injury further thins the depth and experience of an already young and limping group of receivers. Buffalo opened the season with six receivers, including Brad Smith, who doubles as the team's Wildcat quarterback.

And starter Stevie Johnson, who had four catches for 55 yards and a score against the Jets, is hampered by a groin injury that's nagged him for much of the offseason. There are concerns that Johnson will have to continue playing through the pain for the rest of this year.

Rookie third-round draft pick T.J. Graham will get a chance to play after he was left inactive on Sunday. Graham is a raw but speedy player, whom the Bills hoped they could ease into their offense.

Information from The Associated Press was used in this report.