Cashman told ESPN New York that on Tuesday he and Rivera had a conversation in which Rivera said he does not know yet if he will return for a 19th season.
"He wasn't certain on what he is going to do," Cashman said.
After he crumbled to the turf and tore his ACL in Kansas City in early May, Rivera vowed he would return in 2013.
"I'm coming back," an emotional Rivera said in Kansas City a day after the injury. "Put it down. Write it down in big letters. I ain't going down like this."
Now, with his 43rd birthday next month and as he's worked very hard during his rehab to return, Rivera has the familiar tug that he has carried for many years of possibly wanting to stay home with his family and call it a career.
In the past, Rivera also has emphasized that he expects to leave the game as an elite player. If he has doubts that he will retain his skill level, that also could tilt him to call it a career with the most saves (608) in major league history and five World Series rings.
The negotiations for a new contract also could be a bit complicated. Rivera made $15 million last season, but even with the front office's utmost respect for him, it is unclear what it will offer him considering he would be returning after a season in which he pitched in only nine games.
This offseason, the Yankees are beginning to tighten their budget in anticipation of trying to lower payroll by 10 percent to $189 million for 2014. Yankees owner Hal Steinbrenner has mandated the plan to take advantage of the new luxury tax breaks.
During his end-of-season news conference Wednesday, Yankees manager Joe Girardi hinted that Rivera may not return.
"From watching how he rehabbed and everything that he was going through, picked up a baseball sooner than he was supposed to and got his hand smacked a little bit, that would tell me that Mo probably wants to play," Girardi said. "But in saying that, it's a decision that I think he'll sit down with his family, evaluate where he is maybe a little bit later in this process and how he feels and how his arm feels, to feel like you think you can compete at the same level he's always competed at. But I don't think that you push a rehab like he pushed it unless you think that you possibly have some interest in coming back."
Since Rivera already had vowed to come back last May, Girardi's words were taken as managerial-speak, the feeling being Girardi did not want to commit to a player who wasn't signed yet.
In Rivera's place this season, Rafael Soriano thrived as the Yankees' closer, converting 42-of-46 save chances. Soriano could opt out of the final season of his contract. Soriano's agent, Scott Boras, hinted that Soriano would choose free agency but said a final decision had not been made.
"He's one of the best closers in baseball," Boras said. "He had 42 saves, and he didn't start until May."
Rivera has been cryptic about his plans to play or retire. During spring training, he said that he knew whether 2012 would be his last season, but he declined to tell anyone in the front office or the media.
After the injury, Rivera said he would come back for 2013. Now it is still probable, but suddenly it is not certain.