Maine was placed on the 15-day disabled list Sunday with a mild strain in his right rotator cuff. He left Monday's game in Florida after 4 1/3 innings because of pain in his shoulder.
Wagner said he felt pain in his forearm on Tuesday, when he earned his 27th save with a scoreless ninth in the Mets' 4-1 win over Florida. He blew a save chance on Saturday night and said his arm felt strong, but he struggled to locate his pitches.
The Mets didn't make a move with Wagner but the left-hander was unavailable for their game against Houston on Sunday, a 4-0 victory for the Astros. New York is off Monday before hosting San Diego in the opener of a three-game series Tuesday night.
"When you lose Billy Wagner, that's very critical for us," manager Jerry Manuel said.
The Mets purchased right-hander Eddie Kunz's contract from Double-A Binghamton to fill Maine's roster spot. Manuel said before the game the 22-year-old Kunz might be used as the closer Sunday. Instead, Kunz pitched the seventh inning and allowed one hit.
Kunz was 1-4 with 27 saves in 44 games with Binghamton. He threw 17 scoreless innings over his last 16 appearances dating to June 20.
Wagner had an MRI on July 22 that showed muscle spasms around his shoulder joint. But he had tossed 10 consecutive scoreless innings over nine appearances before Saturday night.
"It got to the point where I couldn't locate the ball inside," Wagner said. "The pitches didn't have much finish on them."
The Mets are in third place in the NL East, 2½ games behind Philadelphia and a half-game behind Florida. Wagner was hoping to avoid the disabled list, but also didn't want to come back too soon.
"It's a situation where we're at this part of the season, where you have time to take some time off," Wagner said. "I don't want to hamper the team and continuously fight an uphill battle when we've got it close in the division. There's no use going out there and hurting the team by being something that you're not right now."
Maine's DL stint is retroactive to July 29 and Manuel tentatively plans to start him again at Washington on Aug. 13. Oliver Perez started Sunday's series finale in Houston on regular rest in Maine's spot.
Maine threw a light bullpen session Sunday and said the shoulder felt fine. Manuel said the Mets are just being cautious.
"We know he could use that rest," Manuel said. "The more rest we give him, the better off he'll be."
Maine insisted the injury was nothing serious.
"There's no setback," Maine said. "It's just precautionary. I still feel it a little bit. But it's 100 times better than it was before."