Sudfeld exited Friday's preseason game after his knee buckled while rolling out of the pocket, Joe Person of The Athletic reports.
The 29-year-old was then carted off the field after suffering this injury, per Steve Reed of the Associated Press. Sudfeld is currently fighting for a spot on the Lions' active roster behind quarterbacks Jared Goff and Teddy Bridgewater, and this doesn't help his case. The extent of the veteran's injury is unknown at the moment.