PORT ST. LUCIE, Fla. -- Shortly after Johan Santana took a step toward Opening Day readiness Saturday morning, another member of the Mets' rotation, Mike Pelfrey, became a medical issue. After he was examined by a local doctor, the club learned Pelfrey had suffered a muscle strain in his left lower leg Friday.

The prognosis was unclear following an MRI at a local medical unit. The Mets said Pelfrey would resume his Spring Training preparation when he is free of pain. Mets manager Jerry Manuel indicated an interruption in Pelfrey's spring at this point isn't critical because Pelfey already had pitched -- three innings in two appearances -- and still has nearly a month to prepare.

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Pelfrey was to have pitched Monday against the Orioles, but was told that appearance had been scratched. Pelfrey was hoping at least to play catch on Sunday.

The pitcher, wearing long dark socks, had been walking gingerly in the clubhouse in the morning when he was unsure -- and concerned -- about the redness, swelling and soreness under the skin in the front of his leg. He said there had been no puncture.

"The doctor told me it was a very uncommon injury," Pelfrey said Saturday night, "but that it was one of the better results I could have for an injury in that part of my leg [the front of the leg, about four inches above the ankle]. Before I left [for the MRI], they were throwing around all kinds of possibilities -- shin splits, tendinitis, an insect bite, a rash, an infection, [even] a stress fracture.

"I'm glad it's not a stress fracture. I'd miss a lot of time."

Pelfrey said he was unsure of the cause of the problem, as he didn't participate in morning drills. The club said he had strained the muscle while throwing in the bullpen Friday, but Pelfrey had no recollection of a misstep or an incident.

"That's why it's so weird," Pelfrey said. "[It's] weird to have a strain where it is, and weird because I didn't do anything."

Notes: Right fielder Ryan Church returned to active duty as a pinch-hitter in the Mets' 7-5 loss to the Nationals. Church's severely bruised right knee has improved enough that he will start in Viera against the Nationals on Sunday. ... Second baseman Luis Castillo, his right hamstring not the issue some had feared Friday, is also to play on Sunday. Castillo didn't play Saturday, nor did Angel Pagan (swollen right elbow). Manuel didn't urge Pagan to risk aggravating the injury by playing, but he did indicate that players not assured of a place on the roster -- Pagan is one -- need to perform. The old line for that was: "You can't make the club in the tub," a reference to the old whirlpool baths.