FLORHAM PARK, N.J. -- NT Sione Po'uha, speaking to reporters Monday evening, said he expects to play Sunday against the Bills. He said his back was evaluated last week by the medical staff, which deemed him "four or five days ahead of schedule." He was limited Monday in practice.

"I'm ready to go," Po'uha said. "My job is to make sure I'm well and ready to play. All I've been doing is getting ready and I feel great."

Rex Ryan sounded concerned about Po'uha playing nose tackle, arguably the most physically demanding position on the field, after so much lost practice time. He also is worried about Po'uha aggravating the injury. Po'uha hasn't revealed the specific diagnosis, saying only that it's a stiff back.

"Backs are tricky," Ryan said. "If you go out there too early and have a setback, it can really set you back. He's been getting better ... but he hasn't practiced football. I don't want to say he's ready to go, playing that position. I don't know."

Second-year NT Kenrick Ellis could start in Po'uha's place, but the Jets probably will use their nose tackle a lot less than usual. They won't employ a lot of base defense against the Bills' spread attack; they figure to be in nickel and dime packages most of the game.

Ellis, who spent three weeks in jail before training camp stemming from an altercation while attending Hampton (Va.) University in 2010, received positive reviews for his preseason performance. But the Jets are concerned about the position because they acquired former Dolphins DT Isaako Aaitui on waivers Saturday. Ryan said they will use Aaitui at defensive tackle, not nose tackle.

Aaitui basically will replace Marcus Dixon, who was waived over the weekend. Dixon was a solid backup, which made it a curious move -- even more curious now that we know Po'uha's status is up in the air.

Ryan never gave a definitive reason for cutting Dixon, although he said sometimes young players get the benefit of the doubt. Aaitui is 24, undrafted rookie NT Damon Harrison is 23 and Dixon turns 28 on Sept. 16. Ryan declined to say whether money factored into the decision, deferring the question to the front office. Dixon was due to make $540,000, about $150,000 more than Aaitui.

INJURY REPORT: In other pre-practice injury news, TE Dustin Keller (pulled hamstring) still is likely to play. "Barring a setback, I think he plays," Ryan said ... LB David Harris (sprained ankle) is fine ... RB Joe McKnight, who pulled a hamstring in the preseason finale, told Ryan he'll be ready to play.