Head Coach Jim Schwartz would not comment on an ESPN report the 21-year-old rookie signal-caller suffered a dislocated knee, The Detroit Free Press said Monday.
Stafford, who threw for 296 yards against the Bears, was injured when he was sacked late in the game and was replaced by veteran backup quarterback Daunte Culpepper in the fourth quarter.
"Matt is day-to-day with a knee and we'll see where he is on Wednesday," Schwartz told The Detroit News.
Schwartz said Stafford had undergone medical tests and was listed as day-to-day when practice resumes Wednesday. The 1-3 Lions take on the Super Bowl XLIII champion Pittsburgh Steelers Sunday.
In other injuries, Lions wide receiver Adam Jenkins suffered an ankle injury and linebacker Ernie Sims (shoulder), wide receiver Calvin Johnson (quad) and running back Kevin Smith were all listed as day-to-day.