Betances landed on the injured list with right lat tightness. Matz was placed on the IL with left shoulder discomfort and will see a doctor Monday to determine the next step.
“I definitely felt like I didn’t have anything today,” Betances said.
Manager Luis Rojas said he did not think this injury was related to the lat strain that sidelined him for most of last season with the Yankees.
The Mets signed Betances to a one-year deal with a player option for 2021 in December. The deal will guarantee him $10.5 million.
The New York native is 0-1 with a 6.10 ERA in 13 appearances this season. He is averaging 93.2 mph on his fastball, down from the 97.8 he averaged on the pitch in 2018, his last of five straight seasons with at least 100 strikeouts.
In 2018, Betances made 66 appearances, with a 2.70 ERA and 115 strikeouts in 66 2/3 innings. He was the first reliever in baseball history to have 100 or more strikeouts in five consecutive seasons.
Matz was moved to the bullpen and felt discomfort in a relief appearance on Saturday.
Matz is 0-4 with an 8.63 ERA in six appearances and Saturday was his first time in relief this season. He allowed four combined runs in his first two starts, but was tagged for 19 runs in his next three starts and pulled from the rotation after allowing six runs in a 6-2 loss at Philadelphia on Aug. 15.
Matz made his debut for the Mets in 2015, but he has spent time on the injured list in every season.
He missed nearly two months as a rookie with a lat injury, missed the final month of 2016 with left shoulder tightness and had two stints on the injured list in 2017 with left elbow injuries.
Matz briefly was sidelined in the previous two seasons and Sunday said the injury was a surprise because of how well he had been feeling.
“I was feeling so good coming in,” Matz said. “My arm was feeling really strong and healthy, so I’m pretty bummed about it.”
To replace Matz and Betances on the active roster, the Mets recalled right-handed relievers Drew Smith and Franklyn Kilome from the alternate site in Brooklyn.
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(© Copyright 2020 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)