New York Mets left-hander Steven Matz has been diagnosed with a mild shoulder strain and rotator cuff inflammation during an examination with team doctors in Manhattan and was placed on the 15-day disabled list Monday.

The disabled list move was backdated to Aug. 15.

The Mets promoted infielder T.J. Rivera and right-handed Robert Gsellman from Triple-A Las Vegas for Tuesday's series opener in St. Louis. They replaced Matz and second baseman Neil Walker (paternity leave). Gsellman is expected to be available out of the bullpen.

Steven Matz last pitched on Aug. 14, when he took a no-hit bid into the eighth inning against the Padres. AP Photo/Seth Wenig

Matz had been scratched from Friday's start in San Francisco after experiencing shoulder discomfort. He stayed with the team for the remainder of the weekend, then took a red-eye flight back to New York on Sunday night, accompanied by a team trainer.

Matz next was scheduled to pitch Thursday at Busch Stadium against the Cardinals.

Rookie Seth Lugo is the alternative to face the Cardinals on Thursday, manager Terry Collins indicated Sunday.

Matz already has been pitching with a bone spur in his pitching elbow that will need to be surgically removed after the season.