"His hamstring flared up on him at the end of practice yesterday," McCarthy said.
The coach was not sure if Green will be ready to play on Sunday. "We'll know more in the morning," he said.
If Green, who gained 152 yards on 36 carries in Green Bay's first two games, is unable to play, Noah Herron and newly acquired Vernand Morency are the only other running backs on Green Bay's roster. Both will share in running the ball if Green is unable to play.
Herron has rushed three times this season for a total of 5 yards. Morency joined the Packers last week in a trade from Houston for running back Samkon Gado. He did not play any downs from scrimmage in Green Bay's 34-27 loss to the New Orleans Saints last Sunday, and returned one kickoff for 28 yards. But McCarthy said that Morency took all of the reps in practice on Friday and that he will be more involved with the offense against the Lions.
"I've been getting a lot of reps, just trying to get in tune with the offense," Morency said. "I think everything is going well."
Morency, a second-year pro, said he has worked with running backs coach Edgar Bennett early in the morning and at night to get up to speed with the offense.
"Our main objective is to put everything together and go out there and have fun," Morency said.
Herron has the benefit of working with the offense throughout the off-season and training camp. He led the Packers with 119 yards on 30 carries (4.0 per carry avg.) in the preseason.
Spitz not likely to play
Guard Jason Spitz has yet to practice with the team this week and is not expected to play against the Lions on Sunday. Spitz injured his hamstring in Green Bay's Week 1 game against the Chicago Bears.
Martin returns to practice
Tight end David Martin, who injured his knee Sunday against the New Orleans Saints, practiced with the team on Thursday and Friday, and is expected to play Sunday. Martin to play