"We're optimistic that he'll be back at some point during the season," Yankees manager Aaron Boone said. "I don't want to speculate too much on when."
But Boone added it's "realistic [Gregorius] plays the bulk of the season with us."
Gregorius had an MRI on Thursday that revealed a tear. He and the Yankees are still determining when surgery will be performed.
The team believes it was during Game 2 of the American League Division Series last Saturday in Boston when Gregorius injured his right elbow. The throw that did it came in the seventh inning of a game New York ultimately won 6-2.
On the play, Gregorius hustled into the outfield to field an Ian Kinsler double that ricocheted hard off Fenway Park's Green Monster and out of Yankees left fielder Andrew McCutchen's reach.
Once he picked up the ball, Gregorius threw it back into the infield, where it was cut off as Boston's second run of the game scored.
"Post-game that day, he was in the trainer's room," general manager Brian Cashman said. "Based on his dialogue and the feeling he felt on the tweak there, on that throw was where he pinpointed it."
Gregorius ended up playing through the injury, and finished the series, which Boston won 3-1 to advance to the ALCS.
"If something's bothering him, he's wired in a way that either he just doesn't feel it, or he purposefully conceals it," Cashman said of Gregorius. "He's just the type that he's not going to focus on it, and he's going to go out and do the best he possibly can."
Cashman also said Gregorius had a partial ligament tear that was "asymptomatic" when he was acquired from the Arizona Diamondbacks in December 2014 to be Derek Jeter's replacement at shortstop.
"That [throw] was the finishing off of something that was a sleeping giant, I guess," Cashman added.
Cashman said he had forgotten about the earlier partial tear over the years, but glimpses of throws Gregorius made in Game 4 of the ALDS started to remind him of it. A pair of uncharacteristic short-hops on fairly routine throws caught the GM's attention.
"They were un-Didi-like," Cashman said. "So right away, the back of my mind, I was like, 'Oh, boy. I wonder if we have a real problem here?'"
Like Boone, Cashman declined to give a time frame for Gregorius' return, saying "best to stay general."
Boone said Gleyber Torres could be the Yankees' shortstop to begin the 2019 season. The second baseman, who was a rookie this year, spent time at short when Gregorius was recovering from other comparatively minor injuries he had this season.
"He's very capable of being an everyday shortstop," Boone said.
Torres had his own Tommy John surgery last year after he hurt his non-throwing arm sliding into home while playing in the Yankees' minor leagues. He returned from the midseason injury in time for spring training.
If the Yankees ultimately decide to look outside the organization for help at shortstop, Dodgers infielder Manny Machado, who hits free agency this offseason, could be a possible fit. Cashman didn't answer directly when asked if targeting Machado could now be a more realistic option once this free-agency period opens.
Gregorius batted .268 with 27 home runs and 86 RBIs this season as a big left-handed bat in a lineup heavy with right-handers. He will be entering the final year of his contract in 2019.
"We do expect to get him back," Cashman said. "We do expect him to return to the player that we've obviously been enjoying for quite some time."