Sabathia, who has been sidelined since May 11, had appeared poised to rejoin the Yankees rotation this month before his troublesome right knee swelled after a recent rehab start.
The left-hander, who was 3-4 with a 5.28 earned run average in eight starts before going on the disabled list with a degenerative cartilage problem in his right knee, is set to be examined by an orthopedic surgeon on July 14.
"That’s always a possibility when you have a degenerative knee," Girardi told reporters before Friday's game against the Twins in Minnesota when asked about the prospects of Sabathia needing microfracture surgery.
"It's a surgery a lot of players don't want to hear they need to have. It’s a pretty long rehab."
Asked whether Sabathia's 2014 season could be finished, Girardi said, "That’s fair to say."
The manager said the pitching future of the one-time ace, who led them to a World Series title in 2009, could be in doubt.
"It's too early to predict that," said Girardi. "Whenever you have degenerative issues that cause surgery, there are always questions."
The loss of Sabathia may further motivate the Yankees to explore the trade market for starting pitching as they stood 3 1/2 games behind East Division co-leaders Toronto and Baltimore with the Major League Baseball trade deadline set for July 31.
Sabathia, who has a career record of 208-119, is signed to a five-year deal that ends in 2017 and is worth $122 million.
(Reporting by Larry Fine in New York; Editing by Frank Pingue)