Fister is 3-3 with a 2.45 ERA in 10 starts. The right-hander was scratched from his scheduled outing Saturday to try to alleviate the pain in his shoulder. He said Friday that the shoulder began bothering him after his previous start against Minnesota on Monday. The move is retroactive to June 1.
"As far as medical, nothing has changed," Seattle manager Don Wakamatsu said. "We think that other than him being fatigued, that it's probably smarter to take the time right now and miss two starts. It's just a little bit wiser."
Wakamatsu said team officials had noticed Fister's velocity began to drop during his start against Tampa Bay on May 14, but it wasn't until Friday that they decided to skip his start. It took prodding from Wakamatsu for Fister to admit that he had felt some discomfort in his shoulder since his last outing.
"Just kind of a consensus of both sides with just some fatigue and a little soreness," Fister said Friday. "Probably a better idea to take it off now than it would be to take it off later.
"It's just a little tired and we're giving it a little rest."
The Mariners have used their bullpen heavily the last two games, leaving them short Sunday against the Los Angeles Angels. The lack of available arms helped lead to the decision to place Fister on the disabled list. The team recalled left-hander Luke French from Triple-A Tacoma to help in the bullpen.
"I think it's kind of a combination of the workload in the bullpen but also saying maybe this is the right time to be real cautious," Wakamatsu said. "Our bullpen's really pretty fatigued right now."
Fister ranks third in the American League in ERA.
Wakamatsu said the team hopes Fister will be available for the series finale in St. Louis on June 16.