"He came in today and there's no swelling in there, but he's sore and stiff," Boone told reporters, according to Newsday. "He's just kind of going through treatment right now."
Stanton left the Yankees' 4-3 victory on Tuesday night against the Toronto Blue Jays with a bruised right knee.
He is not in the lineup for Wednesday afternoon's game against the Blue Jays, but he is listed as an available player on the bench.
Stanton was 1-for-1 in Tuesday night's game, hitting a single in the first inning. He got tangled up with Toronto pitcher Clayton Richard while getting thrown out on a headfirst slide into third base, but he remained in left field in the second and third innings.
Stanton is batting .290 this season in nine games for the Yankees. He came off the injured list on June 18 after being shelved since April because of three separate injuries.
The Associated Press contributed to this report.