Bowman, 26, had an MRI done on the knee earlier this week, but the team still has not decided when, or if, he will return this season, ESPN's Ed Werder reports. Werder also reported that Bowman still feels pain in his knee.
Defensive coordinator Vic Fangio said it is possible Bowman does not play this season.
"I think that's a possibility," Fangio said. "I don't know that that's been decided or been the verdict, but I'm sure it's a possibility."
Bowman, a third-round pick in the 2010 draft, had 120 tackles, 5.0 sacks and two interceptions last season en route to making the All-Pro First Team for the third straight year.
San Francisco is 5-4 and in third place in the NFC West. It plays at the New York Giants on Sunday at 1 p.m.
- Paul Palladino