Manager Joe Girardi watched Robertson's session and said the team should decide by Friday if the hurler -- on the disabled list since May 15 with a strained left oblique -- is ready to join Triple-A Scranton/Wilkes-Barre.
"He looked OK, so the next decision is, does he throw in a game or do we have him do one more batting practice before he throws in a game?" Girardi said. "I'm sure that all the powers that be will make a decision pretty quickly."
Girardi said that outfielder Brett Gardner took batting practice on Thursday in Tampa, Fla., and is ready to join Class A Charleston for a Minor League rehab game. Gardner felt some soreness after his last hitting session but reported no problems Thursday.
"I was a little concerned, but the fact that he felt better today, felt good today, makes me feel good," Girardi said. "He hasn't played much in the past month and a half, so I wasn't sure how his arm would feel."