Brian Wilson has strained ribcage

SCOTTSDALE, Ariz. -- San Francisco Giants closer Brian Wilson is being sidelined with a strained ribcage muscle, an injury that could keep the big-bearded major league saves leader out for the start of the season.

The San Francisco Chronicle reported Saturday he had an MRI. Wilson was injured Thursday while pitching against the Los Angeles Angels.

Wilson will be re-evaluated on Monday. It is uncertain whether he will be ready for Opening Day.

If he is out for an extended period, the closer's role likely would be taken by left-handers Jeremy Affeldt or Javier Lopez, or right-hander Sergio Romo.

The 29-year-old Wilson led the majors with 48 saves last year.