Matz was diagnosed with a partial tear of a lat muscle on his left side during an examination on Thursday at the Hospital for Special Surgery in Manhattan.
The Mets placed Matz on the disabled list and promoted infielder Danny Muno from Triple-A Las Vegas.
Alderson said Matz will be reexamined by team doctors in three weeks. If the muscle has healed, he could resume throwing at that point. Otherwise, he will need to refrain from throwing for a longer period.
Matz felt stiffness in the armpit area after his June 28 major-league debut. After consultation between trainers and team doctors, Alderson signed off on Matz proceeding with his second start, this past Sunday at Los Angeles. Matz tossed six scoreless innings against the Dodgers, but again felt pulling in his left armpit area in the final inning.
“But it was never really terrible to where I had to come out,” he said.
The Mets then resolved to skip Matz’s final first-half start and send him for an exam on Thursday, once the team returned from the West Coast trip, according to Alderson.
“It’s never really pain,” Matz said. “It’s just like a little pulling. It’s hard to describe. … It’s definitely frustrating, but it could be worse. It's just a really minor thing.”
Matz added that doctors “wouldn’t jump in front of the door and stop me” from pitching if it were the World Series.
Alderson said he did not agree with Matz’s assessment that the partial tear that showed up on Thursday’s MRI is minor. Still, the GM added that it could have been worse given the potential range of injuries to pitchers.
Alderson said the lat on Matz’s left side is smaller than the lat on his right side, signaling the muscle had atrophied and that the injury may have existed for a while but been asymptomatic.
Allowing Matz to face the Dodgers was made based on the best possible information and not imprudent, Alderson asserted.
“It was assessed by himself as well as based on the information by the doctors as a mild issue at that time,” Alderson said. “If we got an MRI on every pitcher who ever had any sort of mild pain, we’d probably be getting them on a daily or somewhat frequent basis.”
Alderson said it remains unresolved whether the Mets will use a five- or six-man rotation after the All-Star break. However, manager Terry Collins said on the pregame show that a five-man rotation is likely.
If the Mets continue with a six-man rotation after the break, Dillon Gee and Logan Verrett would be candidates to replace Matz. Verrett was demoted this week once Jenrry Mejia was activated from a PED suspension. Verrett will serve as a starter with Las Vegas, but that decision was made irrespective of Matz’s issue. Verrett is on the 40-man roster, whereas Gee is not. Alderson acknowledged “things always tilt toward the 40-man-roster guy.” Still, the GM added that Gee is a “consideration” and there is some roster flexibility to allow the veteran to return to the 40-man roster.
In suggesting it could take more than three weeks for Matz's lat muscle to heal, Alderson pointed to the case of reliever Jerry Blevins, who suffered a fractured forearm bone on April 19. Blevins was forecast to return to the majors in about two months, but a second opinion in Boston on Thursday confirmed his fracture has yet to fully heal. Blevins will not be examined again for three weeks.
Alderson insisted Matz’s injury will not alter his approach at the trade deadline. The GM said he had no intention of dealing from the team's present rotation even before Matz’s injury, despite speculation Niese was available.
“There’s some speculation we were looking to trade pitching, and therefore this loss makes that less likely,” Alderson said. “I don’t think it was ever likely we were going to trade out of that six-man group. … I don’t think that will change our level of aggressiveness. We’re two games over and still in the hunt. … Two weeks ago we didn’t have Steven. It won’t make us less aggressive.”