McCoy is listed as probable on the Bills' injury report.
"I just want to go out there and just see how I feel," McCoy said. "Go out there Sunday and see what I can do. I look forward to playing."
McCoy suffered a Grade 2 hamstring pull in Week 3 and was told it would be a three-to-four week injury. After telling reporters he wouldn't return until he was 100 percent, McCoy declined to put a percentage on his health Friday but believes the Bills' banged-up offense needs him to play Sunday.
"Just how the season has gone, we need this win. It's a big one," he said. "A lot of guys are banged up. Maybe get a big win here, get one more. Go into the bye week and have some time to get healthy. Full week of no running and just treatments. So that's the mindset. Hurt or not, we need this win. So I'm out there for my teammates."
The Bills (3-2) have yet to name a starting quarterback for the game. Tyrod Taylor (knee) is questionable after being limited in practice this week; EJ Manuel would start in Taylor's place if he can't play against the 5-0 Bengals.
"I think he wants to go, there's no doubt about that. But we'll see. He's feeling a lot better," coach Rex Ryan said, adding that Taylor will be a game-time decision.
Harvin practiced fully Thursday, and the Bills were initially going to list him as probable for Sunday's game, but Harvin practiced on a limited basis Friday.
Asked whether Harvin suffered a setback in Friday's practice, Ryan responded, "I have no idea."
Watkins said this week that he wants to play through his injury, even it means aggravating it.