LOS ANGELES — To guard against the bullpen-frying thin air at Coors Field this weekend, the Mets have decided to carry an extra arm. They officially promoted lefty Sean Gilmartin from Triple-A Las Vegas on Thursday and placed utilityman Wilmer Flores on the disabled list with a strained left hamstring.

The move leaves the Mets with only one shortstop on the active roster — Asdrubal Cabrera — but adds a long reliever so that Logan Verrett can make a spot start in place of the banged-up Steven Matz on Saturday.

“It’s frustrating, but what are you going to do?” a bleary-eyed Flores said Wednesday, before he was sent back to New York to be examined.

Flores said he was injured Monday and played through it on Tuesday. But assistant general manager John Ricco said Flores may have injured his hamstring previously in “a couple of different instances.” Either way, Flores’ absence isn’t expected to linger much past 15 days.

“It’s a very mild strain,” Ricco said of Flores, who was hitting just .180 in 19 games. “It bothered him enough that we decided to DL him.”

Terry Collins said Flores could be healthy enough to play in minor-league rehab games in a few days to “get his swing back.”

Verrett has tossed 12 scoreless innings in a pair of spot starts this season. The righthander also shined in Colorado last season in place of Matt Harvey.

Gilmartin, 26, posted a 2.48 ERA in six starts for Triple-A Las Vegas. He returns after he had a 2.67 ERA in 50 appearances for the Mets a season ago.

“I wanted to be here and everything like that,” Gilmartin said. “But once that decision was made for me to be optioned, I put everything I had into helping Las Vegas win games.”

Extra bases

Ricco downplayed David Wright’s flagging arm strength at third base, noting his production at the plate. “When he’s concerned, I’ll be concerned,” Ricco said when asked about Wright’s defense. “But right now, he’s not concerned.” . . . Zack Wheeler is still long-tossing at the team’s Florida complex. He’s still on track to return from his Tommy John rehab in July.