NEW YORK -- What began as a problem has now become something of a catching crisis. And seemingly nobody is immune.

Not 24 hours after starting catcher Paul Lo Duca went on the disabled list with a strained right hamstring, backup Ramon Castro left Sunday's game with mild arthritis of his lower back. He's listed as day-to-day and should be back in uniform -- though perhaps only in limited capacity -- when the Mets begin their road trip on Tuesday in Pittsburgh.

"I was a little bit scared," Castro said after returning from the hospital, where he received treatment and an MRI. "Thank God everything's OK."

Castro said this is the first time he's ever had lower back pain, and he first felt it when he woke up on Sunday morning. By that time, Triple-A catcher Mike DiFelice was en route to Shea Stadium in response to Lo Duca's injury, but a series of flight delays and logistical problems kept him away from the ballpark until after the first pitch.

Castro's pain, meanwhile, was worsening, and by the time DiFelice could stretch and warm up, he was summoned into the game in the top of the fourth inning.

"I can't say that you expect something like that to happen, but you just have to prepare," DiFelice said. "I've played long enough to know that you never know."

That quick pinch allowed the Mets to survive the game -- a 10-4 win over the Marlins -- but just barely. Manager Willie Randolph used emergency catcher David Newhan as his first pinch-hitter off the bench, just an inning after DiFelice entered the game. Another potential option, Ruben Gotay, had started the game at second base, leaving the Mets with a potential disaster should something have happened to DiFelice.

"We probably would have said, 'Raise your hand if you want to catch,'" said general manager Omar Minaya.

No one's had to volunteer yet, but the Mets now have to weigh their options for the immediate future. Assuming Castro's condition doesn't worsen before Tuesday, DiFelice will assume starting duties until Castro is ready to begin playing every day.

Minaya said he won't sign another catcher -- his first choice would be to select Sandy Alomar Jr. from Triple-A -- unless he's forced to place Castro on the DL, and in the meantime, he'll count on his injured backup to be available in a pinch. Lo Duca isn't eligible to return to the team for another two weeks.

"He's going to be where Lo Duca was a couple of weeks ago," Minaya said, referring to when the team essentially played with one-and-a-half catchers for the duration of Lo Duca's first hamstring strain. Castro, like Lo Duca, will be unavailable to start, but his condition shouldn't be so poor that the team needs a third catcher.

Castro was batting .285 with nine home runs in 44 games this season. Yet, nearly half of those games had come since July with Lo Duca battling various injuries, and Castro was batting .317 with five of his homers since that time.

DiFelice, summoned late Saturday night for his second stint with the Mets in two months, didn't arrive at the ballpark until after the game had started. His flight out of New Orleans was delayed by more than an hour, and a lack of other flights forced him to land in Newark, N.J. -- a drive to Shea that took him an hour and a half.

Still, DiFelice quickly loosened up "just in case" something happened, and sure enough, something happened. Now he's facing the prospect of jumping from third to first on the depth chart overnight, and it's a prospect he's ready to embrace.

"I knew that if something happened, I'd be ready," DiFelice said. "I've been ready to catch since birth."