NEW YORK -- CC Sabathia has been placed on the 15-day disabled list with a right knee injury that could end his season.

New York Yankees manager Joe Girardi said Monday there is no timetable for the big left-hander's return, and he kept open the possibility that the 35-year-old Sabathia might not pitch again this year.

The staff leader, Sabathia came out of his start Sunday after just 2 2-3 innings and immediately went for an MRI. The plan is to have Sabathia stay behind when the team goes on their upcoming six-game road trip. The rest of the rehabilitation will depend on how he responds to rest and treatment.

"The MRI really didn't show any changes from before, but obviously he is pretty sore," Girardi said.

Sabathia has been hampered by the knee the past few seasons. He had surgery last year and was limited to only eight starts.

This year, he's slumped to 4-9 with a 5.27 ERA in 24 starts. He's had the knee drained twice and recently received a pain-killing shot, all part of the plan to help him get through the season. Girardi, in fact, was surprised Sabathia wasn't prevented from pitching until he came out of his last start.

"It's been maintenance all year long for us," Girardi said. "We knew that going in and we knew it could rear its ugly head, and he has had some shots before and was able to pitch and it didn't seem to be an issue. But we knew it would take a lot to get him through the season."

The Yankees will be getting right-hander Michael Pineda back Wednesday after a stint on the DL with a forearm strain, and Bryan Mitchell, hit in the face by a line drive on Aug. 17, is nearing a return from the seven-day concussion list. Girardi said Mitchell will go back to long relief.

Girardi also said Sabathia's absence shouldn't affect his plan to use a modified six-man rotation down the stretch to protect their starters.

"We won't need a sixth man every time," Girardi said. "You get to the month of September. If you have to be creative to get the guys an extra day, because you'll have more guys in the bullpen, you can do it that sort of way."