The New York Yankees’ battered rotation may have suffered the most crucial loss of all.

Rookie sensation Masahiro Tanaka, who has 12 wins, has been placed on the 15-day disabled list due to right elbow inflammation. He had an MRI in New York on Wednesday.

Yankees manager Joe Girardi admitted he’s concerned about Tanaka’s prognosis. “You’re always worried when you have a guy go back for an elbow MRI,” he said. “It would be a big loss.”

The Yankees, who have also lost pitchers CC Sabathia, Michael Pineda and Ivan Nova to injuries, are 46-44.

Tanaka allowed five runs and 10 hits — both career highs — in 6 2/3 innings in a 5-3 loss to the Indians on Tuesday night. The All-Star is 12-4 with a 2.51 ERA in 18 starts, but has lost three of his past four outings.

His injury might mean the Mariners’ Felix Hernandez would start the All-Star Game.

Notes

• The Red Sox designated catcher A.J. Pierzynski for assignment. The 37-year-old Pierzynski hit .254 with four home runs and 31 RBI in 72 games this season.

• Royals left-hander Jason Vargas, a former Mariner, was taken to the hospital Wednesday and had an appendectomy. Royals manager Ned Yost said the surgery went great and that there were “no complications.”

• The Yankees’ Carlos Beltran sat out after suffering a facial contusion during batting practice when a ball off his bat caromed off the overhead screen and hit him.

Cliff Lee threw 59 pitches without incident Wednesday in a Class A game in Tampa, Fla., the most positive development in seven weeks for the prized Phillies starter with the strained left elbow. Lee will pitch there again Monday, which could act as a final precursor to his return.

• Cardinals pitcher Joe Kelly is set to return to the rotation Friday from a hamstring injury that’s sidelined him nearly three months.