Stevie Johnson out at least a week
"He's going to be out for a while," Marrone said. "We won't rush to get him back."
Johnson, Buffalo's top receiver, pulled up on a route during a red zone drill two hours into Friday's practice. He was evaluated by Buffalo's training staff and walked slowly to the locker room assisted by two people.
Johnson watched Saturday's practice from the sidelines, according to reports.
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 Bills offense has been hit with a string of injuries this week in practice. According to reports, tight end Mike Caussin missed Saturday's practice after leaving Friday with a hip injury.
Meanwhile, quarterback Kevin Kolb left Saturday's practice after slipping on a wet rubber mat between practice fields. Marrone said Kolb is day-to-day with a "bumped knee."
Information from the Associated Press was used in this report.
MORE NFL HEADLINES
- Rodgers has idea of status, but not saying
- Sources: Welker not expected back vs. Texans
- Harbaugh: 'Absolutely' want to be with 49ers
- Browner vows to sue NFL if ban not dropped
MOST SENT STORIES ON ESPN.COM
THE NFL ON ESPN.COM
- Antigua Men's Buffalo Bills Succeed Royal Jacket