CINCINNATI — An already thin Mets pitching rotation lost a key component Monday as a giant question mark is set to return.

Christian Scott was placed on the injured list with a right hip impingement that isn’t deemed serious, according to manager Carlos Mendoza, and Kodai Senga will return to take Scott’s spot in the rotation Tuesday.

Scott, who has pitched to a 3.10 ERA in nine starts this season, felt discomfort in the hip following his last start and didn’t feel better following his side session Sunday.

A subsequent MRI revealed the impingement.

Scott received a cortisone shot in the hip.

“We’re hoping this is a minimal [absence],” Mendoza said before the Mets lost 12-0 to the Reds.

Kodai Senga is pictured during the Mets’ April 26 game. Corey Sipkin for the NY Post

Enter Senga, who was originally under consideration for another minor league rehab start following a solid outing Thursday for Double-A Binghamton.

The right-hander has spent the past six weeks rehabbing lumbar spine inflammation.

The Mets received promising results early this season from Senga, before a plunge that Mendoza has attributed to the right-hander’s back ailment.

Overall, Senga owns a 9.00 ERA in five starts for the team this season.

He finished last season at Triple-A Syracuse following a second-half nosedive.

In his last minor league rehab appearance, he pitched six innings and allowed one earned run on one hit for Binghamton.

Kodai Senga throws a pitch during the Mets’ April 26 game. Corey Sipkin for the NY POST

“We have been saying we wanted to see results, which we had his last outing,” Mendoza said. “But with him, not only the result but how he feels after he pitches.”

Senga threw a bullpen session Sunday, according to Mendoza, and received the green light a day later.

“He’s ready to go,” Mendoza said. “He’s telling us that he feels 100 percent. He was on board with, ‘Hey, if you want me to go to the minor leagues and pitch again [on rehab], I will do it, but I am ready to compete on the big league level.’ For him to be very vocal about it is a real good thing.”

Francisco Lindor played in a simulated game, receiving at-bats, running the bases and playing defense.

Mendoza said that routine will continue throughout this week before it’s decided if the shortstop, who is rehabbing a calf strain, will need a minor league rehab stint.

Tobias Myers (who started Monday) and Jonathan Pintaro were recalled from Syracuse before the game.

Daniel Duarte was optioned.

Infielder Zack Short was claimed off waivers from the Tigers.