Maine was sidelined from July 29 to Aug. 13 and returned knowing he'd have to pitch with the shoulder problem for the rest of the season. He didn't go more than 5 2-3 innings in his three starts and gave up eight runs on Saturday. His fastball, normally in the low-to-mid 90s (mph), rarely exceeded 89 mph.
Maine said rest helped alleviate the pain the first time he sat out and he hopes another break will allow him to pitch for the final two weeks of the season.
"It's frustrating because I want to be here and help the team.
But for me not being 100 percent to go out there, it's not just hurting the team, it's me not being 100 percent," Maine said. "I was told nothing could make it worse, which is why I wanted to pitch through it. It just hasn't gone away."
Maine said a cortisone shot on Thursday didn't help.
Mets general manager Omar Minaya said surgery is the only way to fix the problem, but even though it's a minor operation, Maine wouldn't have enough time to recover and pitch again this season. Instead, he won't throw for two weeks, and he'll hold off from any exercise for a week.
The NL East-leading Mets, who squandered a seven-game cushion over the last 17 games in 2007 and missed the playoffs, will have to do without Maine (10-8) for at least three weeks, Minaya said.
"We've all seen John Maine. Even without his best stuff, if I'm not mistaken he had a pretty good game in Pittsburgh," Minaya said. "But the bottom line is we cannot risk his long-term health in the midst of this pennant race, which means that guys are going to have to step up."
After a 9-1 victory Monday night over Houston, the Mets own a half-game lead over the second-place Phillies heading into a two-game series in Philadelphia starting Tuesday night.
New York manager Jerry Manuel said Oliver Perez will likely move into Maine's slot on Friday, and that because of a day off Thursday an extra starter will not be needed until Sept. 2.
Maine's injury is the second major blow to the pitching staff.
All-Star closer Billy Wagner has been out since Aug. 3 with a strained left elbow, and his return this season is uncertain. Just as New York has used its existing players to fill that hole, Minaya said a starter probably will come from within the organization, but he didn't entirely rule out claiming a pitcher off waivers.
More likely it will be long reliever Brian Stokes or a minor league pitcher. Top prospects Jonathan Niese and Robert Parnell will be considered. Minaya declined to call up Niese earlier in the season for a start because he didn't want to waste a minor league option on the pitcher for just one start.
But because teams can expand their rosters on Sept. 1, Minaya said Niese or Parnell could get enough action to make a call-up worthwhile.
Castillo, struggling with the hip injury and a sore quadriceps, was batting .261 with three home runs and 26 RBIs when he went on the disabled list July 3. He was given back his spot as the No. 2 hitter and starting second baseman - conditionally.
The Mets went 31-16 without Castillo, who is in the first season of a four-year, $25 million contract, and Manuel has been happy with the platoon of Damion Easley and rookie Argenis Reyes at second.
"We'll watch him play, watch him perform, watch the level the team is playing at with him performing and see where we are," Manuel said. "We are in a fight for our lives."
Castillo went 0-for-4 with a walk Monday night and made a diving catch in the third inning.
