Stafford seemed to be without limitations while reporters had access to practice Friday morning, planting with and jogging on his injured right ankle. Asked if he was healthy enough to play, Stafford said he didn't know.
Stafford limped off the field in last Sunday's loss to Atlanta. He was limited in practice Wednesday and Thursday, then went through a full practice Friday.
"He's better," coach Jim Schwartz said. "Hopefully we can keep him on the track. I don't know officially if he's a game-time decision, but we won't announce anything before then. A lot of things can happen between now and Sunday."
The Lions listed Stafford as questionable on their injury report.
Stafford has played in all seven games this season after missing 13 last year and six in 2009 as a rookie because of injured shoulders and a banged-up right knee. He has completed 60 percent of his passes this season for 1,912 yards with 16 touchdowns and four interceptions.
If Stafford has an unexpected setback, Shaun Hill would start in his place.
Starting running back Jahvid Best will be out for a second straight game with a concussion when Detroit (5-2) tries to snap a two-game losing streak with Sunday's matchup against the Broncos (2-4).
Reserve defensive tackle Nick Fairley, Detroit's first-round draft pick, likely will also be inactive against the Broncos. He aggravated his surgically repaired left foot against the Falcons and was still wearing a protective boot five days later. The Lions listed him as doubtful after he didn't practice for a third straight day on Friday.
"It is going to be something that he is going to have to manage and we are going to have to manage," Schwartz said.