Kelvim Escobar is going back on the Los Angeles Angels' disabled list.

Escobar missed last season with a torn labrum and already spent a stint on the 60-day DL this year because of his troublesome shoulder. The right-hander will be used as a reliever once he returns.

The Angels need to clear a roster spot for right-hander Sean O'Sullivan, who will be called up from Triple-A Salt Lake to start Tuesday night against the San Francisco Giants.

O'Sullivan will pitch in place of Ervin Santana, who will have his turn skipped while he nurses a strained muscle in his forearm. Santana underwent an MRI exam Monday in Anaheim before flying to the Bay Area.

Escobar is eligible to come off the DL next Monday and manager Mike Scioscia thinks he should be on schedule. Escobar likely will pitch the eighth inning but also could be an option to close out games.

"It's moving forward and we'll know once he starts throwing," Scioscia said. "I would be very surprised if he's not in our bullpen next Monday. I don't think there's any problem if we throw him right in there. Naturally, in a perfect world, we'd like to ease him in there. We desperately need that kind of arm in our bullpen."

Santana's forearm began bothering him after his last start Thursday night at Tampa Bay, when he allowed six runs and eight hits over 4 2-3 innings in an 11-1 loss.

Scioscia believes he will come back strong after some extra rest. Santana pitched well in a win at Detroit on June 5, a positive sign for Scioscia.

"I think if we hadn't seen him throw the ball as well as he did in Detroit and seen his stuff pick up, we might not be as comfortable in where he's going to be," he said.

Also Monday, slugger Vladimir Guerrero began a throwing program as the outfielder continues to work himself back from a torn right pectoral muscle that has limited him to designated hitter duties. He wasn't in the lineup for the series opener against the Giants in an NL park.

He threw from 75 feet.

"Vlad doesn't have light catch in his toolbox," Scioscia said. "He goes all out."