SAN FRANCISCO -- Giants closer Brian Wilson, who's striving to recover from a strained oblique muscle in his left side, is likely to begin the regular season on the disabled list, manager Bruce Bochy indicated Monday.

"I'll be honest -- I think it's less than 50-50," Bochy said when asked about Wilson's chances of being on the active roster when the Giants open their defense of their World Series championship Thursday at Los Angeles. "But we're not going to rule him out completely."

Sidelining Wilson wouldn't necessarily put the Giants at a huge disadvantage. They could backdate the right-hander's disabled-list assignment for up to 10 days, which could render him eligible for activation as early as April 5.

Make no mistake: the Giants will activate Wilson as early as possible.

"Wilson's the caliber of closer that it's a little bit of a kidney shot when he goes down," left-hander Jeremy Affeldt said. "Whoever's closing that night is just filling in. You're never going to replace him."

But the tenuous nature of oblique injuries, which can recur without thorough healing, has prompted the Giants to be careful with Wilson, who led the Major Leagues with 48 saves last year before he added six in the postseason.

"Obviously we want him there and we're pulling for him to be there," catcher Buster Posey said. "But at the same time, we want him to be 100 percent healthy when he comes back."

Moreover, time is running out for Wilson to build up sufficient arm strength to handle his role. His anticipated bullpen session Tuesday will mark the first time he has thrown on a surface other than flat ground since March 17, when he made his last of five Cactus League appearances.

Bochy said that he has decided which reliever or combination of relievers he'd use in the closer's role if Wilson is sidelined.

"But I'm not prepared to announce which way we're going to go," Bochy added.

Should Bochy prefer to rely on a sole reliever, he'd likely call upon right-hander Santiago Casilla, who complements a 95-mph fastball with a wicked curveball, or Affeldt, who has the most Major League closing experience among San Francisco's setup men. Affeldt and Casilla saved four and two games last year, respectively.

Or Bochy, who seeks advantageous matchups and plays occasional hunches, could employ the closer-by-committee method. In that event, right-hander Sergio Romo and left-hander Javier Lopez would join the contingent. So would right-hander Guillermo Mota and left-hander Dan Runzler -- if they make the 25-man roster, as has been speculated.

"I think we have enough guys of different types and enough depth so that if we have to go out-by-out, we will," Affeldt said.

Bochy said that Wilson played light catch Monday at the team's training facility at Scottsdale, Ariz. Wilson's bullpen stint, which also will occur in Scottsdale, probably will last eight to 10 minutes.

"We're not going to push him if he doesn't feel great," Bochy said. "But so far in his throwing sessions on flat ground, he hasn't felt anything."