ST. LOUIS — Perhaps, he’s being overly optimistic. But Mets manager Terry Collins left open the possibility that lefthander Steven Matz misses only his scheduled start on Thursday before coming off the disabled list.

“Right now, the way it looks, it’s going to be the one start,” Collins said. “It’ll be Thursday. We’re hoping that by Tuesday, he’ll be OK to go again. But we’ll just have to wait and see.”

The Mets placed Matz on the DL retroactive to Aug. 15 with what they have labeled as left shoulder tightness. It’s a relatively minor issue, especially considering the range of more severe possibilities when it comes to shoulders.

“I take it as good news,” Collins said. “Certainly, any time you’ve got a pitcher especially with a shoulder issue, you’re on pins and needles, not knowing how bad it’s going to be. So, it came back that it was good news. Hopefully, a few days off and a little bit of rest will get him ready for next week.”

To replace Matz, Robert Gsellman was promoted from Triple-A Las Vegas. He threw 3 2⁄3 innings for the win after replacing Jonathon Niese (knee) in the first inning Tuesday night.

Walkers welcome daughter

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Neil Walker and his wife Niki welcomed their first daughter into the world at 3:06 a.m. on Tuesday, when Nora Vail Walker arrived weighing seven pounds, three ounces.

The Mets placed Walker on paternity leave, which allows him to be away from the team through Thursday. But Collins said Walker is expected to call on Wednesday to discuss if the second baseman can return earlier.

T.J. Rivera was promoted from Triple-A Las Vegas to take Walker’s spot. Rivera started at second base and batted sixth for the Mets on Tuesday night.

In turn

Monday’s off day gave the Mets the flexibility to alter their starting rotation, especially with crucial games that will shape the wild-card race. But Collins defended his decision to keep the rotation in line, even if it means starting the likes of Jonathon Niese and Seth Lugo.

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“We don’t need anybody to get hurt,” Collins said. “So, let’s just keep them in turn, use the extra day, and keep them rested up. That’s my thought on the whole thing.”