Steven Matz will not start for the Mets on Thursday because of continued shoulder stiffness that the Long Island lefty on Tuesday called “irritation in the rotator cuff.”

Matz, who was scheduled to come off the disabled list to face the Marlins on Thursday, felt the stiffness when he tried to throw on Tuesday. He will rest and get treatment, and while Matz and the Mets say they hope he can return this season, it’s not clear that he will be able to.

“I don’t quite feel like I can let it go yet,” Matz said. “So [I] talked to them and the training staff and that’s the decision, to just get some more rest. Let it calm down. . . . The doctor said everything structurally looks OK. Just classic impingement, I guess, it what you can call it.”

The Mets are calling it more bad injury luck. Manager Terry Collins said he hoped he’d see Matz on the mound again this season, but admitted he’s concerned that isn’t going to happen.

“Yes, I am,” Collins said. “We’ve had him looked at. The reports are there’s no structural damage, so we’re not worried about rotator-cuff stuff, we’re not worried about torn labrums. We’re worried about a stiffness in his shoulder that is keeping him from being confident that he can pitch. . . . He’s too valuable down the road to just continue to push it and say, ‘You’re going out there anyway.’ ”

Collins may not have had the latest information when he said Matz didn’t have a rotator cuff issue. Matz, who spoke after the manager informed the media of the new problem, said he’s been told “this is not a surgery-type deal.”

Matz, who is already pitching with a bone spur in his elbow that may require surgery after the season, said: “I felt like I was making progress and then I threw off the mound a little bit [Sunday] and I felt OK coming out of there. And [Tuesday] I tried to throw and it was barking at me a little bit again. It didn’t cause me to stop throwing because I was able to get my tossing in, but for me to get on the mound and throw a bullpen and be ready in time for a game would just be unrealistic in my mind.”

Collins said Jacob deGrom would replace Matz on Thursday. DeGrom had his most recent start skipped because of ineffectiveness. He was originally slated to return on Friday.

Matz said the “barking” began again when he tried to throw a curve.

“Now it’s just kind of a discomfort when I throw,” Matz said.

Still, Matz said he is holding out hope he can pitch again this season.

“Yeah, I believe so,” the 25-year-old said. “I think it’s a day-to-day thing. The doctor believes that I can pitch again [this season] with the results of the MRI.”

Matz, who is 9-8 with a 3.40 ERA and last pitched on Aug. 14, said “there’s no way of telling” if the shoulder woes are related to his elbow injury.

“My arm was really feeling great, which is really why it’s a big disappointment because I was really feeling really good,” he said. “A few days after throwing that last game I threw, something just started barking at me and it hasn’t really subsided since.

“I would say it’s really frustrating. You want to stay on the field. You want to be able to compete and that’s something I’ve kind of battles this year, so it’s definitely frustrating.”