The move was made retroactive to Sunday, a day after Maine was tagged for seven runs and six hits over a season-low four-plus innings in New York's 7-1 loss at the woeful Washington Nationals.
"It's nothing serious," he said. "My shoulder is just fatigued. It's dead."
General manager Omar Minaya said team doctors examined Maine on Thursday and found "fatigue in his shoulder and some shoulder weakness."
"I can't give you a timetable on him because it's going to be a rehab situation," Minaya said after New York lost 6-3 to the Philadelphia Phillies in 10 innings. "It may need to be rest and it could be some type of exercise to strengthen the shoulder."
Maine joins fellow starter Oliver Perez (right knee tendinitis), slugger Carlos Delgado (right hip) and speedster Jose Reyes (right calf) on the Mets' crowded DL. Key reliever J.J. Putz also is out after elbow surgery.
New York had said before the game that Maine would get an extra day of rest before his next outing, with Livan Hernandez moving up to start the Subway Series opener Friday night against the New York Yankees. The Mets were off Monday, so Hernandez will be working on regular rest.
Minaya said he is looking at several possibilities for Saturday's start.
Manager Jerry Manuel said before Thursday's game he was unaware of Maine's shoulder problem, saying he thought his difficult start against Washington stemmed largely from a stomach flu that swept through the clubhouse recently.
"There was no indication to me that that was a serious issue for him," Manuel said before the loss against the Phillies. "We'll watch him carefully because he is coming off of surgery."
Maine was 5-1 with a 2.36 ERA in his last seven starts before the shaky outing against Washington. He is 5-4 with a 4.52 ERA in 11 starts on the year.
Maine had surgery Sept. 30 to shave a bone spur in his right shoulder, and struggled with his mechanics in the spring.
"I've been full-go throwing since basically December. It's telling me to back off a little bit," Maine said before the loss to the Phillies.