PITTSBURGH — Anthony Rizzo was scratched with lower-back stiffness prior to Tuesday night’s 5-2 loss to the Pirates at PNC Park.

Rizzo’s left-handed power has been key to the Yankees’ success and is second on the team with 22 homers — trailing only Aaron Judge.

Aaron Boone said Rizzo couldn’t get loose prior to the game, which is something he’s dealt with in the past and typically keeps him out one or two games.

“It might end up being a couple days,’’ Boone said.

Asked his level of concern about the injury, Boone said, “I don’t think a ton.”

Rizzo had homered in three of four games before going hitless in Sunday’s loss to the Guardians in Cleveland.

Rizzo missed time last year shortly after being traded from the Cubs due to a bout with COVID, but hasn’t been on the IL with an injury since 2018.

He was slated to start at first base. He was replaced at first by DJ LeMahieu, with Gleyber Torres going to second base from DH and Matt Carpenter added to the lineup as the DH.

Jonathan Loaisiga (right shoulder inflammation) threw another live batting practice at the team’s player development complex in Tampa on Tuesday, according to Boone.

Boone said Loaisiga is scheduled to throw another side session before a potential rehab appearance with Low-A Tampa on Saturday.

If all goes well, Loaisiga could meet the team in New York next week, with more possible rehab appearances with Double-A Somerset or Triple-A Scranton/Wilkes-Barre.

Miguel Castro remains away from the team on the paternity list. Boone said he could be back Wednesday.

Domingo German is scheduled for at least one more rehab start as he looks to return from right shoulder impingement that has sidelined him since spring training. Boone said the right-hander “looked sharp” in his most recent outing for Double-A Somerset, when he threw about 50 pitches. Depending on what the Yankees’ needs are in the coming weeks, German could use the entire 30 days of his rehab window.

“We’re encouraged by his direction,’’ Boone said.

The team announced that catcher Austin Wells, among their better prospects, was promoted to Double-A Somerset from High-A Hudson Valley. He’d been on the IL with a groin injury and was rehabbing with Low-A Tampa. In 155 plate appearances combined between the two spots, he has eight homers and an OPS of .993.

Manny Banuelos, traded to the Pirates for cash considerations after being designated for assignment by the Yankees last week, is expected to join Pittsburgh on Wednesday.

“I’m excited for him to have an opportunity,’’ Boone said of the former Yankees prospect, who hadn’t pitched in the majors since 2019 before his comeback with the Yankees. “He can pitch. I’m not surprised somebody claimed him. It was great having him here this spring and when we called him up [to the majors], he earned the opportunity.”

Gerrit Cole was slated to take the mound Wednesday and make his first start in Pittsburgh since the January 2018 trade that sent him to Houston, but the Yankees’ rainout last Friday in Cleveland pushed back the $324 million ace’s outing to Thursday’s opener of the Yankees’ four-game series in Boston.

“I had it circled, but hopefully with the schedule change in the next few years how the divisions shake out differently, I’ll have another opportunity coming up soon to pitch here,” Cole, who pitched for the Pirates from 2013-17, told reporters before Tuesday’s game. “It would be special.”

Bill Mazeroski, who beat the Yankees with a game-winning home run off Ralph Terry in Game 7 of the 1960 World Series, threw out the first pitch before Tuesday’s game.

— Additional reporting by Peter Botte