KANSAS CITY, Mo. — The Yankees’ Giancarlo Stanton began a rehab assignment at Double-A Somerset on Tuesday night, though New York manager Aaron Boone said that it was too early to tell when the slugger might return to the big leagues.

Stanton has missed the entire season because of severe tendon injuries to both of his elbows. But he has been ramping up his work at the Yankees’ player development complex, and Boone was optimistic the rehab assignment will not be long.

“He’s playing tonight. Probably play tomorrow. And then we’ll see about Thursday, if he plays again or what we want to do through the weekend,” Boone said before the Yankees opened a three-game series against the Royals.

“Just kind of taking these two-day increments,” Boone said.

The 35-year-old Stanton only appeared in 114 games last season, but he hit .233 with 27 homers and 72 RBI. He was at his best in the playoffs, when he hit seven homers over 14 games and was voted the MVP of the AL Championship Series.

“For him, it’s just getting his body built up and him being in a position to where he knows he’s had enough at-bats and enough reps to be game-ready, to be season-ready,” Boone said. “And he’s had a pretty big ramp-up. He’s had a lot of at-bats already, even going into his rehab start tonight. So, just making sure he’s had the necessary reps and feels really good.”

In other injury news, right-hander Marcus Stroman is expected to make a rehab appearance for Somerset on Wednesday as he works his way back from left knee inflammation that has sidelined him since a start April 11 against the Giants.

Jake Cousins was pulled off his rehab assignment after the right-hander felt something amiss in his right elbow.

Cousins, who has been dealing with a strained right forearm, underwent an MRI exam, Boone said, and the plan was to visit with Yankees team physician Dr. Christopher Ahmad in the hopes of determining exactly what went wrong.

The reliever made six appearances for New York in the playoffs last season.

“I mean, considering he was into his rehab and build-up and now to feel something with the elbow, it’s concerning,” Boone said. “But again, I don’t want to overreact. We don’t have any information.”