Sean Manaea dealing with an oblique strain, has been shut down indefinitely

Mets left-hander Sean Manaea has a right oblique strain and has been shut down indefinitely, manager Carlos Mendoza said Monday morning.

The injury to Manaea is the second major blow to a Mets rotation that is already without Frankie Montas until at least the middle of May.

Mendoza said Manaea had been feeling the issue since the beginning of camp, and initially kept throwing live bullpen sessions through it. But with Manaea unable to turn the corner regarding the injury, he was sent for an MRI on Sunday that revealed the strain.

“The good news is this is not — the tendon is not involved, the rib cage is not involved,” Mendoza said. “It’s just straight muscle, so he’s going to be shut down for a couple of weeks — and then we’ll reassess after that. We’ve gotta build him back up again. Safe to say that he’s probably gonna start the season on the IL.”

Mendoza added: “It could take seven, 14, 21 days to heal. And then once he’s symptom-free, he’ll start his throwing.”

With Montas and Manaea both out, the Mets’ starting pitching depth is being seriously tested.

“We still feel really good with what we have internal,” Mendoza said. “With Manaea, I’m not overly concerned.”

Speaking after Mendoza, Manaea said his absence could be anywhere from “a couple of weeks to a couple of months.”

Regarding whether the Mets were still planning to go with a six-man rotation, Mendoza was non-committal.

As things currently stand, the Mets’ starting rotation to begin the regular season is expected to include Kodai Senga, Clay Holmes, and David Peterson.

Options to fill the fourth, fifth, and potentially sixth spots on the starting staff include Paul Blackburn, Griffin Canning, and Tylor Megill.

Max Kranick, a former starter who is in camp, has been transitioning to a multi-inning relief role.

An option to help in the rotation at some point this season is prospect Brandon Sproat, but it seems highly unlikely he’ll be on the big league roster on Opening Day.

If the Mets decide to seek external starting pitching help, there are still a handful of options on the free agent market, including Lance Lynn and Jose Quintana.