Buffalo Bills defensive end Chris Kelsay sacks Arizona Cardinals QB Kevin Kolb in Week 6. Kelsay has been out after tearing a ligament in his neck at practice. (US Presswire)

Buffalo’s defense has finally started to live up to its potential, and it looks like it will get a key contributor back in the lineup for a big Week 12 matchup against Indianapolis.

Veteran DE Chris Kelsay returned to practice Monday on a limited basis after missing Buffalo’s last two games with a neck injury.

“I tore a ligament in my neck,” Kelsay said. “It was kind of a freak deal. It happened at practice. There’s no real rhyme or reason, just turned funny and strained it. I rested it, I feel a lot better than I have been feeling and I’m looking forward to getting back out there and helping my teammates get on this run.”

"We’ll find out what he can do Wednesday, but it looked promising," coach Chan Gailey said.

Kelsay, who had been replacing injured starter Mark Anderson at right defensive end, may have a hard time receiving a starter’s share of reps even if he is back to 100 percent against the Colts. DEs Kyle Moore and Shawne Merriman impressed in Week 11 in his absence, notching one sack apiece. Moore, in particular, has been explosive off the edge and may have been Buffalo’s top all-around DE in the win over Miami.

Either way, Kelsay’s glad he can join his teammates in what will be a pivotal game for the Bills. At 4-6, the Bills are chasing the 6-4 Colts for one of the final wild card spots. A loss could sink their faint playoff chances for good.

“Everything still lies ahead of us this week ... the way our schedule will play out, who we’re facing, a lot of people who are right in the same spot or maybe ahead of us, we play,” Kelsay said. “So if we play up to our potential, the way we’ve been playing really the last couple weeks, we’ll be in really good shape.”

Jackson to be cleared Tuesday: RB Fred Jackson (concussion) is expected to be cleared to return Tuesday, Gailey said. Jackson missed Buffalo’s Week 11 win over Miami due to the injury. “Supposedly he’ll complete everything tomorrow,” Gailey said. “Everything’s on track for him to be ready to go Wednesday.” Jackson, who splits time with C.J. Spiller, has 298 yards rushing and 183 yards receiving in seven games.

Injury roundup: Five Bills did not participate at practice on Monday -- Jackson, WR Brad Smith, DT Spencer Johnson, DE Mark Anderson and CB Aaron Williams. Smith and Johnson are expected to return to practice Wednesday. Anderson and Williams haven’t been ruled out for Sunday, but both will have a difficult time making it, according to Gailey.

Caussin placed on IR: The Bills had until today to decide whether to activate TE Mike Caussin off the PUP list or place him on injured reserve, and with Caussin not yet back to 100 percent, they decided to put him on the shelf for the remainder of the year. Caussin suffered a serious knee injury late last season. “He practiced for three weeks and he never got appreciably better,” Gailey said. “He told me in his own words he was 75 to 80 percent, and that’s not good enough. We weren't going to release him, so we just put him on IR. He played for us last year and showed a little promise. It’s a shame all that happened for him the way it did. Hopefully, he'll get better and be able to play again.”

For more updates on the Bills, follow correspondent Mark Ludwiczak on Twitter @CBSBills and @MarkLud12.