The Mets placed the right-hander on the 10-day DL with a strained left hamstring and recalled infielder Matt Reynolds from Triple-A Las Vegas. Reynolds was expected to join the Mets in time for Wednesday night's game at Miami.
Assistant general manager John Ricco said the Mets have full faith in the training and strength and conditioning staff, despite a wave of injuries this year.
"It's easy to start painting a broad brush as to the reasons," Ricco said of the injuries. "You get frustrated, but as an organization we have to take a logical approach to it. We have a lot of confidence in the guys on the medical side. As a team they're as good a group as there is."
After Gsellman was hurt, Mets broadcaster Ron Darling blamed an emphasis on weightlifting by team trainers.
"Get them in a room with some of the old trainers and people who took care of baseball players on how to keep them healthy," said Darling, who pitched in the majors for 13 years. "Get them in a room and try to tap into their knowledge on how to train baseball players. Not weightlifters. Not six-pack wearers. Baseball players.
"They're doing a disservice to the million-dollar athletes they are paying. It's a joke to watch this happen each and every night."
Gsellman (5-5, 6.16 ERA) was hurt trying to beat out a grounder Tuesday against the Marlins. His injury means right-hander Rafael Montero (1-4, 5.63 ERA) will remain in the rotation.