Stafford separated the same shoulder in the season opener and missed the next five games.
Lions coach Jim Schwartz said Monday that the two injuries aren't related, but the team plans to be careful with Stafford.
MLive.com reported Tuesday that preliminary tests on Sunday showed Stafford had a Grade 3 separation of the shoulder and the team fears he might be lost for rest of the season.
None of Detroit's quarterbacks were in the locker room Monday when it was open to reporters, although Stafford later told WJR Radio he doesn't think he'll play this weekend at Buffalo.
Schwartz said Stafford had an MRI on Monday and that surgery wasn't being discussed, but that it's too early to determine the severity of the injury. According to MLive.com's report, it is not known if the MRI results confirmed the team's initial diagnosis.
"I think I just, all our tests and consultations and everything else, I just won't comment anymore on," Schwartz said. "He'll be thoroughly evaluated."
According to MLive.com, Stafford is expected to get a second opinion from Dr. James Andrews, who consulted with the quarterback after his first shoulder injury this season.
Despite Stafford's injuries this season, Schwartz said he doesn't question the quarterback's durability.
"He hasn't been able to play as much as he'd like to play, but he hasn't been hampered by hangnails or, you know, headaches or anything like that. He's been hit by 290-pound guys going full speed."
Rookie wide receiver Michael Moore, who played with Stafford at Georgia, was more than willing to vouch for Stafford's toughness.
"We played Kentucky a couple years ago," Moore said. "He took a shot to the face without a helmet on and he was bleeding out the face, and he came back in the second half and we won the game."
Stafford has started 13 games as a pro, with six touchdown passes and one interception in limited action this season. The Lions (2-6) clearly are improving, but their top quarterback has played only one full game this season.
Stafford also missed six games as a rookie with a banged-up left shoulder and a sore right knee.
If Stafford is out, the Lions don't necessarily know who their starter would be. Drew Stanton relieved him Sunday, but only because Shaun Hill, who started the five games Stafford missed earlier this season, was still recovering from a broken arm that knocked him out of a game three weeks ago against the New York Giants.
Schwartz said Hill could potentially be ready by this weekend, but the Lions have a lot to consider over the next couple days.
Rayner, a Michigan State alum, was drafted in 2005 by Indianapolis. He's played for five NFL teams, not including the Lions. He was released by Cincinnati in September.
Hanson's injury Sunday forced 307-pound Ndamukong Suh to try an extra point, which hit the right upright, costing the Lions a point they could have used later when the Jets tied the game on a last-second field goal. Suh grew up playing soccer, and Schwartz said he was prepared to kick in an emergency, but the coach said he probably should have called a timeout to give his defensive lineman some time to warm up.
"I put him in a bad position," Schwartz said. "It was a crucial extra point in the game -- probably worth a timeout."
According to the NFL, the last defensive lineman to make an extra point or field goal was Green Bay's Dave Pureifory, who made an extra point on Sept. 29, 1975.
Schwartz also addressed comments by Jets linebacker Bart Scott that the Lions played dirty Sunday. Both teams were penalized 11 times.
"You probably have to consider the source," Schwartz said. "Rather than talk about Bart Scott, let me talk about a really classy guy in Trevor Pryce. Trevor Pryce was the guy that ran into Jason Hanson and got Jason Hanson hurt. Trevor Pryce sought me out after the game to apologize. ... To me, that's a very classy player and I think that speaks a lot about the Jets."
On Tuesday, the Lions released cornerback Jonathan Wade and center Cody Wallace and announced cornerback Jack Williams will stay on the reserve-physically unable to perform list for the rest of the season.
Wade started the first four games of the season but was a reserve for the last four.
Information from The Associated Press was used in this report.