Stafford, who sustained the injury to his right shoulder during Sunday's 23-20 loss to the New York Jets, had an MRI exam on Monday, and it is not known if that test confirmed the team's initial findings.
Stafford is expected to get a second opinion from Dr. James Andrews, just as Stafford did earlier this season for a previous shoulder injury. MLive.com reported that no decisions about Stafford's status for the rest of the season have been made yet.
"I've got to talk some more with these doctors and kind of figure out what they're thinking," Stafford told a Detroit radio program Monday night. "It's kind of frustrating to be coming back and, two games later, be knocked out again. We'll take it day by day and figure out what the plan is."
Stafford's first shoulder injury this season was a Grade 2 separation, and it kept him out six weeks. With eight weeks remaining in the regular season, a Grade 3 separation likely would prevent Stafford from playing again in 2010.
Stafford said his current injury felt "very similar" to his first shoulder separation.
"We don't share results of MRIs or anything else with members of the media or anybody else other than the player and the staff here," Schwartz said. "Matt wasn't able to finish the game; he was very sore, and we'll get him back on the field as soon as we can. And that's been our approach with reporting injuries from the very beginning."
On Monday, Schwartz said that surgery wasn't being discussed, but that it's too early to tell how severe this injury is.
"I think I just, all our tests and consultations and everything else, I just won't comment any more on," Schwartz said. "He'll be thoroughly evaluated."
Stafford is dealing with his fourth injury in less than two years. He missed two games with a dislocated right knee cap, and then after playing two games with a separated left shoulder, sat out the final four games of the 2009 season.
"I don't question his durability at all," Schwartz said. "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."
The Associated Press contributed to this report.