The Yankees on Monday looked ahead to the start of the ALDS vs. the Guardians. Manager Aaron Boone talked about his confidence in the lineup and slugger Aaron Judge talked about the learning experience in falling short over the last several years. Credit: Newsday/Thomas A. Ferrara

Missing the ALDS could be the least of DJ LeMahieu’s worries. It’s certainly the least of Scott Effross’.

LeMahieu and Effross were left off the Yankees’ Division Series roster Tuesday, but LeMahieu could potentially miss the entire postseason, and Effross, who will have Tommy John surgery, will likely be out for more than a year.

The do-it-all infielder missed nearly all of September with what the Yankees called toe inflammation, but according to a report in the New York Post, LeMahieu is actually nursing a broken foot. Aaron Boone wouldn’t confirm the diagnosis — he said he didn’t know the exact injury — but took a grim tone when relaying that LeMahieu’s batting practice swings Monday showed he wasn’t ready to return. The manager repeatedly described LeMahieu as “compromised.”

“He wanted to give it a go and was willing to give it a go, and just like, ‘I feel like I can give you an at-bat off the bench and give you a routine play,’  ” Boone said before Game 1 of the ALDS against the Guardians at Yankee Stadium on Tuesday.

“But just watching him, he is really compromised, and I just felt like it wasn’t the responsible thing to do.”

Boone said it was possible this would rule him out for the ALCS. “We’re leaving the door open,” he added.

Meanwhile, Effross’ diagnosis came as a surprise — perhaps to the reliever most of all. Effross felt some lingering discomfort after an appearance against the Orioles on Sept. 30 but bounced back in his regular-season finale against the Rangers on Oct. 3. He threw live batting practice during the workout Friday and had “mild soreness” that trainers believed was sticking around too long, he said. An MRI on Saturday revealed the UCL tear.

“I was a little taken aback,” said Effross, who was acquired from the Cubs at the Aug. 2 deadline and contributed immediately, with three saves and three holds for the Yankees in their closer-by-committee framework.

“You know when you go in [the MRI that] there’s the possibility of finding something you don’t want to see. For me, I think it was kind of shocking .  .  . I was really not expecting that.”

Effross’ loss is significant to a bullpen limping to the finish line. Clay Holmes is returning from a shoulder injury that caused the Yankees to shut him down in the final week of the season. However, Holmes pitched pitched the final two-thirds of an inning for the save in the Yankees 4-1 win over Guardians in Game 1 of NLDS Tuesday night.

Wandy Peralta (thoracic spine tightness) hadn’t pitched in a month and Ron Marinaccio’s shin injury kept him off the roster.

Holmes threw a bullpen Monday and looked good, Boone said, and Jameson Taillon and Domingo German were also available in relief. This doesn’t even take into account the other bullpen no-shows, a who’s who of once-key pieces who got hurt or underperformed: Chad Green, Zack Britton, Aroldis Chapman and Michael King.

Effross (2.54 ERA) said he hasn’t scheduled his surgery, but that he’ll likely be out for the typical 12 to 18 months. Surgery is always a blow to a pitcher’s career, and it might be more so in his case: Effross was quickly establishing himself as a reliable arm, and, at 28, he has only one year of major-league service time.

“It’s a huge loss,” Boone said. “Feel terrible for him. He’s kind of heartbroken over it. It’s a blow. I mean, Scotty came over here and pitched really well. I think he was going to have a really big role for us in our bullpen .  .  . Somebody else has to pick up that slack.”

LeMahieu’s injury, on the other hand, takes away a solid bat and nips at the Yankees’ versatility. It’s likely also the reason why Marwin Gonzalez — who can play first if Anthony Rizzo comes out of the game — was chosen over Oswald Peraza, the impressive rookie shortstop.

“It was a close call,” Boone said. “I just think the versatility — Peraza’s kind of like [Tim] Locastro, that second pinch runner .  .  . There was a strong case for everyone. And in the end, this is the way I wanted to go.”

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