Andy Pettitte’s stiff back will keep him off the mound for a while longer.

The left-hander’s next start is now scheduled for Friday in Toronto after the Yankees decided to postpone a bullpen session yesterday.

“He’s better,” manager Joe Girardi said. “But instead of saying, ‘Let’s throw a bullpen today and see how he feels’ and then if he has a setback, then Friday becomes jeopardized. We thought we’d give it till [tomorrow for the bullpen sesssion], when we feel everything is cleared up.”

Ivan Nova, who had been skipped after his outing was rained out Wednesday in Cleveland, will get the start tomorrow, followed by CC Sabathia and Phil Hughes.

“I’m on board with it to a certain extent,” Pettitte said. “I want to pitch. I understand it. I feel a ton better. I just want to pitch and get back out there as soon as I can.”

Pettitte was excellent in each of his first two starts, but initially felt something in his back during his appearance in Cleveland on Tuesday. After the 40-year-old was sent back to New York early, his back stiffened up again as he tried to get off the couch at home.

He insisted he had no say in the decision.

“I pretty much told them how good I felt [Saturday] and how much better I was feeling,” Pettitte said. “They said, ‘OK, you’re pitching Friday.’ That was pretty much it. ... We’re going to be conservative. We’ve got guys that can pitch.”

Pettitte admitted the discomfort lasted beyond Thursday.

“I was still tight Friday,” Pettitte said. “It’s just getting better and better every day. I feel real good today and plan on continuing to feel really good.”

* Eduardo Nunez was held out of the starting lineup again for last night’s 3-0 victory over the Orioles with a bruised right wrist after being hit by a pitch on Friday, but he and Girardi expect him to be at shortstop tomorrow against the Diamondbacks.

“I sure hope so,” Girardi said.

Nunez was able to play catch yesterday, but didn’t take any swings.

“I’m getting better every day,” said Nunez, who was also hit by a pitch the previous Friday in Detroit. “It’s just a bad week. I have to forget about it.”