The Detroit Lions placed running back Jahvid Best on the physically unable to perform list.
Monday's designation prevents the 23-year-old from playing in the first six weeks of the regular season.
Best's season last year was cut short due to concussion problems.
A 2010 first-round draft pick of the Lions, Best has rushed for 945 yards and six touchdowns in 22 career games.
Joining Best on the PUP list is rookie cornerback Chris Greenwood. The fifth- round pick hasn't been cleared for practice since tearing an abdominal muscle in OTAs.
The Lions also placed offensive linemen Jonathan Scott and Bill Nagy on injured reserve, while releasing wide receiver Dominique Curry and safety Isaac Madison.