TEMPE, Ariz. -- Ervin Santana, the All-Star right-hander of the defending American League West champion Angels, has been shut down after an MRI traced discomfort in his pitching elbow to a sprained medial collateral ligament.

Santana, who went 16-7 for the 100-win Angels and was signed to a four-year contract the day before reporting to Spring Training, had been scratched from his first scheduled Cactus League start a couple of days ago. Three days earlier, he had felt soreness at the end of his one-inning outing in an intrasquad game.

The pitcher himself seemed unaware of the seriousness of the injury, earlier brushing it off as "inflammation."

"I was worried before talking to the doctor [Lewis Yocum]," Santana said. "I thought it could be worse. I thought maybe I'd need surgery. I'll start playing catch next week."

Manager Mike Scioscia, however, felt the issue was serious enough to rule out Santana's availability at the start of the season. He is set to open the season on the disabled list.

"We'll slow him down, let the stuff in his elbow calm down, and go from there," Scioscia said. "We don't anticipate that it's the sort of setback that will cost him an appreciable part of the season."

But Santana being ready for the season now is "a bit of a stretch," Scioscia added.

As such, the Angels' season-opening rotation will have two holes, with Jon Garland, a 14-game winner last season, having gone to Arizona as a free agent.

Scioscia is confident that the depth of starting pitching at the Angels' disposal will pick up the slack, just as it did last season, when senior starter John Lackey didn't make his first start until May 14 due to a strained right triceps.

Dustin Moseley and Nick Adenhart filled in for Lackey's absence then. The two right-handers had been competing for the fifth slot in this season's rotation. Now, with Santana's injury, they're vying for the No. 4 slot in the season-opening rotation.

"We have guys we feel will be able to do the job," Scioscia said. "And with [Kelvim] Escobar back [from missing the entire 2008 season with a torn labrum], we feel we're in good shape."

A healthy return by Escobar, who had been 18-7 in 2007, would be a huge boost. But he hasn't yet appeared competitively this spring and is also on a conservative schedule. The club doesn't expect him back at the Major League level until at least mid-May.

Santana's activity during the offseason in the Dominican Winter League might become an issue in the wake of his injury. To the Angels' knowledge, he appeared in only two games, throwing a total of 6 2/3 innings. But according to some Winter League insiders, he actually made four appearances and logged 16 innings. His Dominican League and Angels teammate Erick Aybar confirmed that.

Santana said he felt fine when he arrived in camp and did not feel any discomfort until his intrasquad outing Tuesday. He didn't see his season-opening availability as out of the question.

"I think I'll be ready for that," said Santana, contradicting Scioscia's caution. "But he's not in my mind. It's already a lot better. Right now, I don't feel anything."

Santana had previous elbow problems, back in 2004, when he was with the Angels' Double-A Arkansas club and tendinitis knocked him out for the season after eight starts.