PITTSBURGH -- In what the Mets believe will be only a temporary blow to their stretch-run rotation, the team placed Max Scherzer on the 15-day injured list Wednesday, four days after he exited a start due to left-side fatigue. Both Scherzer and Mets manager Buck Showalter downplayed the severity of the injury, predicting he will return as soon as he’s eligible on Sept. 19.

“This is days, not weeks,” Scherzer said. “That’s the first and foremost thing. This is not a significant injury.”

It is, nonetheless, the three-time Cy Young Award winner’s second trip to the IL this season. The 38-year-old missed time in the first half with a left oblique strain, which he called unrelated to his current issue. Until Saturday, Scherzer’s oblique hadn’t bothered him since the early days of July. An MRI taken Tuesday also came back negative for muscle strains. The official diagnosis is “left oblique irritation,” which Scherzer described as an “achy” feeling.

“I don’t have one specific spot that you can point to where that hurts,” Scherzer said. “It’s just general fatigue on the whole left side.”

For days, the Mets held out hope that Scherzer might avoid the IL, but Wednesday forced their hand for multiple reasons. Per MLB rules, it was their final opportunity to backdate an IL stint to Sunday, allowing Scherzer to return as soon as Sept. 19. Placing Scherzer on the IL also cleared space for the Mets to recall two relievers, right-hander Yoan López and lefty Alex Claudio, in time for their doubleheader against the Pirates. (López served as their 29th man.)

Those moves patched up the bullpen, even as the rotation remained in flux. While the Mets haven’t announced a starting pitcher for Friday’s game against the Marlins, David Peterson -- who has filled in admirably on multiple occasions this summer -- is the most likely candidate. Trevor Williams is a fallback option. Carlos Carrasco and Taijuan Walker are also in line to pitch this weekend, but concerns exist there as well; Carrasco is coming off a poor start in his return from the injured list, while Walker is dealing with a blister issue.

Such troubles exacerbate the concern over Scherzer’s injury, minor though it may be. The IL stint comes at a time when New York is engaged in a tight race with the Braves for the National League East title. The two clubs are tied atop the division after Atlanta defeated the A’s and the Mets lost to the Pirates on Tuesday, marking the first time all season the Braves have held at least a share of first place.

“There’s nothing you can do about it,” Scherzer said. “I’ve got to deal with what I’ve got. I had a little hiccup. Tried to work around it. I didn’t let it become something big. It just became a bigger hiccup.”

Scherzer began feeling left-side soreness during the fourth inning of his last start against the Nationals. Initially, he attempted to pitch through it, before alerting the training staff out of concern that he could make the situation worse. After that outing, Scherzer said he expected to make his next start.

His personal feelings regarding the injury haven’t changed much in the interim. While Scherzer did agree that it seems prudent for him to skip a start, he believes he could have made his next one after that. But the Mets, given their pitching crunch, thought it wiser to place Scherzer on the IL, giving him more time to heal while also allowing them to bring in pitching help. Scherzer said he planned to refrain from throwing for “a few days” before restarting a program this weekend in Miami.

In a best-case scenario, the schedule gives Scherzer a chance to make three more starts before the playoffs, including one in Atlanta in the final days of the season.

“All things considered, I think it’s best to get that completely healed again,” Showalter said.

Signed to a three-year, $130 million contract last offseason, which set an MLB record with a $43.3 million average annual value, Scherzer has gone 9-4 with a 2.26 ERA, a 0.92 WHIP and 153 strikeouts over 127 2/3 innings. He had his Opening Day start pushed back a day due to hamstring tightness and he missed around seven weeks earlier this season due to a left oblique strain. Scherzer also lost time last year due to groin and triceps issues, as well as an “overcooked” pitching arm that prevented him from making his final playoff start for the Dodgers.