The injury-beleaguered Mets received another dose of bitter news Thursday when lefthander Steven Matz was diagnosed with a partially torn lat muscle in his left side.

The Ward Melville product will be shut down from all throwing for three weeks, the Mets announced, making him the latest critical member of the team to miss extended time.

After Matz's last start on Sunday, manager Terry Collins revealed that he experienced tightness in his lat region after his big-league debut on June 28. But Collins did not express concern about the injury.

Neither did Matz, who insisted after allowing two hits in six shutout innings against the Dodgers on Sunday that the lat issue did not impact his performance.

"Once I got out there, it was feeling good," said Matz, who is 2-0 with a 1.32 ERA since his promotion from Triple-A Las Vegas. "And it still feels good now."

Treatment, Matz said, was enough to help him deal with the tightness.

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But his status has since changed.

After an examination on Thursday at the Hospital for Special Surgery, Matz had a platelet-rich plasma (PRP) injection, a procedure that has become increasingly popular and typically is used to speed up the healing process in damaged tissue.

He was scheduled to start in Sunday's first-half finale against the Diamondbacks. Instead, he most likely will be replaced by lefthander Jonathon Niese, according to a source.

Matz's injury continues what has been a consistent pattern with the Mets, who have downplayed health problems only to watch them become more serious issues.

The cycle presented itself in the case of third baseman David Wright and catcher Travis d'Arnaud, both of whom remain on the disabled list.

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The injury dampens what had been a charmed few weeks for Matz. He had become the latest elite pitching prospect to reach the big leagues with the Mets, joining Matt Harvey, Jacob deGrom and Noah Syndergaard. He also had been a force at the plate, going 3-for-6 with five RBIs, including four in his debut.

Matz was a member of a six-man starting rotation, which had been designed to manage the workloads of the team's young starters. But with Matz's looming absence, it's unclear how the Mets will adjust.

Dillon Gee could be promoted from Triple-A Las Vegas to take Matz's spot in the rotation. Calling up Gee, however, would require the Mets to create a spot on their 40-man roster.

The upcoming All-Star break buys the Mets some time to reshuffle the starting rotation in Matz's absence.