The Mets starting rotation in 2017 has been much like a revolving door: When one pitcher enters, another hits the disabled list.

New York took another big hit on Monday, as Steven Matz was diagnosed with an ulnar nerve injury similar to that of Jacob deGrom‘s last season, and the southpaw will require surgery.

While deGrom has come back looking just as strong as ever, the state of the rotation is very much up in the air.

“You can never have enough,’’ Collins said about the seemingly nonstop pitching injuries. “If there was one common denominator it is something that can be fixed, but this just tells you anything can happen at any time. There are no guarantees in this game.’’

In fact, No. 48 has been the only constant in the Mets rotation this season and is the only one not going to be coming off injury next year.

Matt Harvey, going into his contract year, struggled Monday night for Double-A Binghamton as he continues to regain his footing from Thoracic Outlet Syndrome surgery last year.

Tommy John surgery is looming for Seth Lugo, who was pitching with a partially torn ulnar collateral ligament all season and just went down with a right shoulder impingement.

It was a struggle for former first rounder Zack Wheeler all season, who registered a 3-7 record with a 5.21 ERA in 17 starts for the Mets before going down with a “stress reaction” in his right arm. There is currently no timetable for his recovery.

The Mets are keeping their fingers crossed Noah Syndergaard can pick up right where he left off, but the big righty has been working his way back from a partial tear in his right lat muscle and may not return this season.

For what many fans deemed “The Big Five,” things have certainly took a turn for the Mets this year whose pitching proved to be their downfall.

“We really came into this season saying that we were prepared for it if somebody was injured,” Collins said. “We had seven guys, five of them went down and all of a sudden the backups were guys we had to go find. You have to keep as much pitching around as you possibly can.”

Sandy Alderson has attempted to stockpile his farm with flame throwing bullpen arms, but the rotation remains in flux.

A lot is going to have to break right for the Mets in 2018 if they once again plan to rely on their starting as their key to victory.

The cat with nine lives, Rafael Montero, looks like he may be turning a corner and Robert Gsellman turned in a solid outing on Monday, but the sample sizes are too small to reach a conclusion on the aforementioned two.

Chris Flexen may be an important arm in the future for New York, but he’s only up here because of all the injuries after making the jump from Double-A Binghamton.

Beyond him? Tyler Pill. That’s about it. Not exactly inspiring.

As much as they need to fill holes around the diamond with the departure of several crucial veterans, it may be time to bring in external reinforcements to bolster the rotation.

If they sit on their hands yet again, we might see Groundhog Day: Mets Edition in Queens next year.