Though saying he's optimistic, running back LeSean McCoy wasn't prepared to announce whether his injured left hamstring will be healed in time for the Buffalo Bills' season opener against Indianapolis on Sept. 13.

"I feel good. It's just a matter of time," McCoy said Friday, while acknowledging he is still experiencing some pain when making certain cuts.

"We'll wait and see, see how everything plays out," he added, when asked how confident he was of playing. "I'm always confident. But I think it does matter that you're confident in your ability to make cuts."

McCoy spoke after taking part in limited on-field drills during a light practice for the first time since being hurt on Aug. 18. McCoy was previously limited to working out on the sideline under the observation of the training staff.

Coach Rex Ryan would only reiterate that he remains cautiously optimistic McCoy will be ready to play.

The NFL's 2013 yards-rushing leader was acquired in a trade with Philadelphia this offseason to be the centerpiece of a run-heavy attack Ryan and new coordinator Greg Roman are introducing to Buffalo.

The injury has the potential to limit McCoy, who is noted for being a speedy and shifty runner.

Before he was hurt, McCoy complained of being rusty after having six carries for 16 yards and added an 8-yard catch in Buffalo's preseason-opening 25-24 loss to Carolina.

He'll now get the weekend off to rest. The Bills don't return to practice until Tuesday.