The Detroit quarterback hurt his right shoulder again late in his team's 23-20 overtime loss to the New York Jets on Sunday.
With the Lions leading 20-10, Stafford was tackled trying to scramble deep in his own territory and landed on the shoulder. He separated the same shoulder in the season opener and missed the next five games, not returning until last week's win over Washington.
It's not clear how serious this latest injury is.
"He's very sore," coach Jim Schwartz said. "We took enough time with it that we thought that, any re-injury would be a new injury. We'll see where he is with that."
Stafford, the No. 1 pick in last year's draft, headed to the sideline with 5:19 to play Sunday and was replaced by Drew Stanton. Stafford threw for two touchdowns and ran for one before hurting himself.
"That was a tough situation because he had green grass in front of him and had his chance to break out of there and run," Schwartz said. "But some of those plays we just need to throw it away. We didn't want to throw incomplete passes in those situations. He ran it."
Backup Shaun Hill has been recovering from a broken arm suffered three weeks ago against the New York Giants, which is why Stanton was pressed into service as the game slipped away.
Copyright 2010 by The Associated Press