NEW YORK -- Mets right-hander John Maine has been diagnosed with right rotator cuff tendinitis, according to a team release. He will begin a rehabilitation program and will resume throwing as tolerated.

Maine, who was placed on the 15-day disabled list Friday with what the team termed right shoulder weakness, underwent an MRI on Monday that revealed tendinitis in his shoulder. Maine said Friday that he expected to come off the disabled list next month, when he is eligible.

"I guess they want to get to the bottom of what's going in there once and for all," said Maine, who vocally disagreed with his assignment to the disabled list. "I feel that I'm more than capable of going out there every five days. But it's not my decision."

Maine has admitted to pitching with varying degrees of pain over the past two seasons. When the Mets removed him from last Thursday's start after five pitches due to concern over his lack of velocity, pitching coach Dan Warthen called Maine "a habitual liar" in matters regarding his health.

"There's a little bit of pain, but what pitcher doesn't have pain?" Maine said. "It's the nature of pitching. It wasn't going to stop me from going every five days."

The Mets plan on skipping Maine's upcoming turn in the rotation Wednesday against the Phillies. They are likely to tap Raul Valdes when they next need a fifth starter on Saturday.

The Mets also announced Monday that they have reinstated infielder Daniel Murphy from the 15-day disabled list and optioned him to Triple-A Buffalo. There, the Mets plan on exposing Murphy to first base, second base, third base and both corner outfield positions in an effort to increase his versatility.