The comments reflect McCoy's desire to play at 100 percent, as expected, but also the reality that the hamstring injury is not fully healed yet.
After Friday's practice, when asked by reporters about his availability for the Bills' season opener Sept. 13 against the Colts, McCoy said, "We'll wait and see."
"See how everything plays out," he said. "Only thing I can do is control what I can control, and that's just working hard and getting treatment and getting ready to go get out there."
Added Bills coach Rex Ryan: "I'm hoping that he will be available to us. And I think the only thing I mentioned was 'cautiously optimistic,' and I remain optimistic."
McCoy agreed with Ryan's comments, saying, "Well, me too. Me too. Like I said, I feel good; it's just a matter of time."
Earlier this week, a team source told Anderson that the Bills were concerned McCoy might not be fully ready for Week 1. According to the source, McCoy had suffered a "small tear" in his hamstring and, while he was rehabbing and conditioning, was not at full speed in practice. The source said if McCoy is ready and plays, the team would consider putting him on a "pitch count" or even holding him out if he's not 100 percent.
Microscopic tears can occur in even less serious hamstring injuries.
Ryan said Friday he wasn't aware McCoy had suffered a tear.
McCoy participated in practice Friday for the first time since injuring his hamstring Aug. 18. He took part in individual drills, the only portion open to reporters. He later said he didn't do too much running or cutting in practice.
Earlier this week, Ryan cast some doubt on whether McCoy would be able to play, saying, "Well, we certainly expect him to go, I hope," adding the Bills would rely on the "next man" if he can't play.
Asked Friday who the "next man" would be, Ryan said, "I'm not gonna get into those type of scenarios, the what-ifs and all that type of stuff. I know one thing: This football team will be ready. Period."
Information from ESPN's Josina Anderson and Mike Rodak was used in this report.