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Routine procedure for 49ers' Willis

Patrick Willis cited a minor knee ailment when withdrawing from the Pro Bowl last month.

The linebacker underwent a bursectomy to address the problem in his right knee, the 49ers announced. This appears to be a routine procedure.

Colts quarterback Peyton Manning underwent knee surgery for something similar before the 2008 season. Manning's bursa sac was infected, however. Willis' was not.

49ers team doctors Tim McAdams and Gary Fanton performed the surgery on Willis at Stanford Hospitals and Clinics in Redwood City, Calif., according to the team.