Robert Gsellman last pitched on Sunday, Aug. 11, 2019, when...

Robert Gsellman last pitched on Sunday, Aug. 11, 2019, when he allowed two runs in one-third of an inning in the Mets' 7-4 loss to the Nationals.   Credit: Jim McIsaac

KANSAS CITY, Mo. — Already short on reliable late-inning options, the Mets’ bullpen lost one of its stalwarts Saturday when Robert Gsellman landed on the injured list.

Gsellman is dealing with a tight right triceps and had been active but unavailable for the previous couple of days. The 10-day IL stint is retroactive to Wednesday, so Gsellman will be eligible to return next weekend as the Mets host the Braves.

Before the Mets made the transaction decision Saturday, Gsellman played catch at Kauffman Stadium, team and player hoping the issue would subside. He hasn’t pitched since last Sunday, when he allowed the Nationals two runs in one-third of an inning.

“It felt pretty good (when Gsellman played catch), but at this point, we can’t run him out there,” manager Mickey Callaway said. “So we decided to do the right thing, take care of him for a few days.

“When it’s something like that where it’s just a little soreness, you want to see if the stiffness and soreness goes away. But after a few days, we felt that this was the necessary move.”

The Mets brought up Walker Lockett, a righthanded starter, from Triple-A Syracuse to take Gsellman’s roster spot and fill in in the bullpen. Callaway said the Mets opted for Lockett, who has been the club’s No. 6 starter when needed this season, over a reliever because Lockett will “give us the best chance, give us the best innings and protect us with some length.”

Of the Mets’ cadre of relievers who have bounced between the majors and minors this season, none have pitched well enough to stick.

“Somebody has to step up,” Callaway said. “It’s like everything else. When somebody goes down, somebody else has to step up. You can’t really worry about it. It’s something that’s happened. Hopefully, Walker or somebody else will step up and get some big outs for us.

“(Lockett is) a guy that’s going to go in and throw strikes, maybe get us a ground ball if we need one. He can get multiple outs. So at this point, I think it’d be a multiple innings-usage thing right off the bat and then we’ll kind of adjust.”

This season, Gsellman has a 4.66 ERA and 1.37 WHIP in 63 2/3 innings, fourth in innings among major-league relievers. In discussing bullpen workloads early this season, Callaway expressed a desire to push Gsellman (and Seth Lugo, who has been healthy and effective) to around 100 innings.

Davis out

A day after being removed from the game with a tight right calf, J.D. Davis was out of the lineup Saturday. He said he felt “very good,” but Callaway decided to play it safe. He pinch hit in the seventh for Joe Panik and struck out.

“J.D. came in today feeling a lot better,” Callaway said. “Just to make sure we’re doing the right thing, he’s not going to be in the lineup.”

Since the All-Star break, Davis was second in the NL in average (.379) and OBP (.440) heading into play Saturday. He is batting .429 during his career-high 10-game hitting streak and has been the Mets’ everyday leftfielder since Dominic Smith (left foot stress reaction) got hurt.

Aaron Altherr, the Mets’ only reserve outfielder, started in left Saturday.

Extra bases

In the Mets’ win Saturday against the Royals, Seth Lugo — not Edwin Diaz — picked up the save with a perfect ninth inning. Diaz pitched the previous two days, so Lugo was more rested. Callaway has oscillated between the dominant Lugo and the struggling Diaz in save situations lately ... Amed Rosario (0-for-3 with a walk) served as the DH for the first time in his major-league career Saturday. Callaway said he considers the amount of recent physical stress on players in deciding who doesn’t have to play the field this weekend, so Rosario, who has been on base a lot lately, got the nod … Brandon Nimmo (bulging disc) did not play Saturday after beginning a rehab assignment with advanced Class A St. Lucie.

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