PITTSFORD, N.Y. -- Buffalo Bills wide receiver Stevie Johnson left practice after injuring his left hamstring Friday morning.
Johnson, Buffalo's top receiver, pulled up on a route during a red zone drill two hours into practice. He was evaluated by Buffalo's training staff and walked slowly to the locker room assisted by two people.
Bills coach Doug Marrone said after practice that he did not know the severity of the injury and that Johnson will be evaluated by Buffalo's doctors. According to NFL Network, Johnson was going to undergo an MRI.
"It would be a major concern when we talk about it during the season, but right now, I think a veteran player that has proven himself, we'll just see what the doctors say and it is what it is," Marrone said. "We'll deal with it from there."
Johnson has had some issues with injuries in recent years. He missed several spring practices due to a back injury and underwent groin surgery last offseason.
Any prolonged absence would be a concern as Buffalo tries to establish a fast-paced, up-tempo system under new offensive coordinator Nathaniel Hackett. Johnson is the team's only established receiver and has had three consecutive 1,000-yard seasons. Last year, he led the Bills with 1,046 yards receiving.
The injury does present an opportunity for Buffalo's young receivers. The Bills took Robert Woods 41st overall and Marquise Goodwin 78th overall in the draft, and both have enjoyed strong training camps thus far.
Goodwin had the play of the day to finish practice on Friday, streaking down the left sideline for a 60-yard touchdown pass from rookie QB EJ Manuel. Woods has impressed with his precise route-running and is the favorite to land the No. 2 receiver job.
"I look at it as an opportunity to get those younger guys more reps," Marrone said.
Tight end Mike Caussin also left practice Friday with a hip injury. Caussin missed all of last season due to a torn ACL.
The news was better for standout pass rusher Mario Williams. Williams is nearing a return to practice after missing the start of camp due to a sore foot.
"It's getting closer," Marrone said of Williams. "He did a little bit more today, he's going out there, going through the walkthrough, so now we're just waiting for the doctor to release him and then he'll be going out there."
Information from The Associated Press was used in this report.