Mets relief pitcher Robert Gsellman bends over in pain as...

Mets relief pitcher Robert Gsellman bends over in pain as a Mets trainer assists him off the field during the eighth inning of an MLB game against the Orioles at Citi Field on Tuesday. Credit: Kathleen Malone-Van Dyke

Robert Gsellman’s season is over due to a broken rib suffered during his 74-pitch relief outing Tuesday.

The Mets put Gsellman on the injured list Wednesday, recalling righthander Drew Smith to take his place. The diagnosis disappointed Gsellman — and shocked manager Luis Rojas.

“I was actually really, really surprised. Because it’s a rare injury,” Rojas said. “Last night we thought it was the oblique. We left thinking it was the oblique. And then this morning when I got the call from our head trainer, Brian Chicklo, he told me about the fracture I was very, very surprised. It’s a rare injury there. It’s just an unfortunate loss for us.

“He was emotional. Obviously, it was a tough season for him in those two ways, health-wise and performing-wise. We wish G to a prompt recovery and he can come back healthy and strong and perform like we know he can. He was very emotional about it. It’s just a tough one.”

It is not clear how, exactly, the injured happened. Rojas said he didn’t know. The Mets did not make Gsellman available for an interview.

In relief of Michael Wacha, Gsellman was on mop-up duty and having a tough time, allowing six runs in 3 2/3 innings. After his 74th pitch — his most in nearly three years and 22 more than his most recent start before he was demoted back to the bullpen — he crouched over in pain and left the game.

This is Gsellman’s third injury in 13 months, after a partially torn lat cost him the end of last season and a tight right triceps cost him the beginning of this one. Upon his return, he made one relief appearance, was inserted into a Mets dilapidated rotation, made four mostly poor starts and put back in the bullpen.

Now, he is done for the year. He had a 9.64 ERA, allowing 15 earned runs in 14 innings across six games.

“Finishing his season like this is definitely a tough one,” Rojas said. “He worked really hard for this. He didn’t get the result he wanted. We didn’t get what we wanted from him as well.”

Lowrie still a mystery

If you are holding out hope that Jed Lowrie might return this year, perhaps you shouldn't.

Is Lowrie doing any sort of baseball activities?

“I don't know what he's doing,” Rojas said.

Lowrie — diagnosed with PCL laxity, which means one of his knee ligaments is loose — has been receiving a series of platelet-rich plasma and stem cell injections in his left knee for about the past month, according to the Mets.

“The timeline of it, I'm not very much aware,” Rojas said. “I know there were going to be different injections to the knee that were going to heal it.”

In the almost two seasons since signing a two-year, $20 million contract with the Mets, Lowrie is 0-for-7.

Extra bases

Rojas said lefthander Steven Matz (left shoulder bursitis) and righthander Dellin Betances (tight right lat) are expected back “soon,” though their specific timelines are “uncertain.” Matz threw a two-inning simulated game Tuesday. Rojas said the Mets aren’t sure if they want to build him up to starter-length again . . . Even beyond pitching Friday, when he’ll leapfrog Seth Lugo to stay on normal rest, Jacob deGrom will stay on an every-five-days starting schedule, Rojas said. The Mets will arrange the rest of the rotation around him . . . The Mets’ three active Puerto Ricans — Lugo, closer Edwin Diaz and bullpen coach Ricky Bones — wore No. 21 in honor of Robert Clemente Day on Wednesday.