PORT ST. LUCIE, Fla. — Steven Matz will be sidelined for more than a month with his latest elbow ailment, opening the door for Zack Wheeler to crash the Mets’ starting rotation after a bumpy two-year absence following Tommy John surgery.

“It’s been a long road,” said Wheeler, who received the news Thursday just before the Mets broke camp and headed for New York.

Wheeler, 26, began camp on the fringes of the competition for a roster spot, but his fastball returned to life, hitting 97 mph on the radar gun. And despite a 5.11 ERA in camp, he improved in every start.

“It’s been a long trek for him,” general manager Sandy Alderson said. “We felt that if he was on an uptick physically, emotionally, it would be a real positive for him to begin the season and not be relegated to Port St. Lucie again. So he’s feeling good and we feel good about it. So we’ll get him right out of the gate.”

Matz, 25, found himself on the opposite trajectory. Elbow soreness wiped out what was supposed to be the Long Island native’s final spring training tuneup. When he made an effort to get on the mound again, the pain persisted.

His latest MRI exam found no structural damage to his elbow, but Alderson said he underwent a platelet-rich plasma injection to promote healing.

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Doctors recommended that Matz be shut down from throwing for three weeks. After that, he must complete a throwing program, which would push his absence to a little more than a month at least.

“I don’t know if I have the words for it,” manager Terry Collins said. “I’m disappointed.”

But the Mets have touted their rotation depth, which again should come into play. Wheeler and Seth Lugo had been the candidates for the opening left by Matz, and the nod went to Wheeler, who last started a big-league game on Sept. 25, 2014.

The following spring, Wheeler tore a ligament and tendon in his right elbow. The Mets hoped he would be back by last July, but repeated setbacks wiped out his second full season. After experiencing elbow soreness early in camp this year, he only gained momentum.

“I’m here, I’m healthy and I want to pitch,” he said. “And that’s what I’m about to be able to do.”

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Wheeler will be under an innings restriction, but the Mets have backed off a cap of roughly 120 innings. Instead, Alderson said there will be some flexibility in that number. It’s part of the reason the Mets were comfortable with starting Wheeler in the rotation rather than in extended spring training or in the minors.

“We have a target, but targets move, so I think it will depend a lot on how he’s performing and how he’s feeling,” Alderson said. “We’ll try to build in a little flexibility. I don’t think he’s going to pitch 200 innings.”

Wheeler will start April 7 against the Marlins as the club’s fourth starter. Noah Syndergaard will follow with his second outing of the season, followed by fifth starter Robert Gsellman, who will be available in the bullpen for the first few games.

Wheeler will pitch in an intrasquad game Saturday as a tuneup. He will remain in Florida along with Matt Harvey, who also will pitch in a scrimmage Saturday.

The Mets have yet to decide between Lugo and Rafael Montero for the final spot in the bullpen.