"We'll see," Caldwell said. "He's very, very sore. There's no question about that. He got hit far too many times."
To be fair, Caldwell typically answers in some form of noncommittal fashion when it comes to the availability of players, particularly early in a game week. This isn't a red flag yet as far as Stafford's availability for Sunday's prime-time game against the Broncos.
But Stafford has taken a large number of hits during the first two weeks of the season and has suffered injuries to his throwing arm, chest and ribs. The Vikings officially sacked him once but hit him at least eight times Sunday.
Stafford had X-rays taken of his chest and ribs after Detroit's 26-16 loss to Minnesota on Sunday, but Caldwell would not divulge the results of the X-rays or say whether anything is broken. Stafford often grimaced after hits and was clearly in pain in the locker room after the loss.
Stafford has completed 51-of-83 passes for 532 yards, four touchdowns and three interceptions.
In the Lions' locker room Monday during media availability, he appeared to be moving better, and he didn't seem to have any wraps on his chest or ribs, although his left elbow was still bandaged. He declined to comment on his injuries in the locker room, saying he would talk Wednesday, his typical podium day.
Later, on WJR radio in Detroit, Stafford said "I feel OK" and was asked if he would play Sunday. He wouldn't say whether he would play against the Broncos, but said, "My intention is to get as ready to practice this week and see what happens."
The Lions' first practice of the week is Wednesday.
Caldwell did not rule out potentially signing a third quarterback this week. The Lions have only two quarterbacks on the active roster -- Stafford and Dan Orlovsky. Orlovsky has not thrown a pass in a regular-season game since 2012, when he completed 4-of-7 passes for 51 yards in one game for Tampa Bay.
The Lions have Ricky Stanzi on the practice squad. When asked if the Lions would consider signing Stanzi off the practice squad or bringing in a free-agent quarterback, Caldwell would answer only the Stanzi question, saying "certainly." But the coach did not answer the question about bringing in a veteran free agent.
Caldwell said the decision of whether Stafford will play Sunday would likely begin with the doctors. Caldwell said it happens in that order to take the feelings of coaches and players out of it.
"We kind of make it pretty cut-and-dried," Caldwell said. "If the doctors tell us that they can play, that they are capable of playing without getting further injury or things of that nature, obviously, then obviously that's when we are given the task of determining how we fill out our 46-man roster.
"But with guys and the ability to play, they don't let him go unless he's ready to go, OK. So the same thing will happen with Matthew this week."
Stafford, who has played his entire career with the Lions, hasn't missed a game since the 2010 season.