Giancarlo Stanton homered in the sixth inning of Game 1...

Giancarlo Stanton homered in the sixth inning of Game 1 of the ALCS on Saturday, Oct. 12, and apparently strained his right quadriceps soon afterward.   Credit: Newsday/J. Conrad Williams Jr.

HOUSTON — For everything championship-quality about the Yankees this season, there has been another less desirable part of their DNA: their alarming fragility.

And it was that defect that again showed itself at the worst possible time, before Sunday night’s Game 2 of the ALCS, when Aaron Boone revealed that Giancarlo Stanton was out indefinitely with a right quad strain.

Though this was hardly expected, it really shouldn’t be surprising, based on the Yankees’ terrible luck in the health department and Stanton’s numerous injuries, which limited him to 18 games this season.

The Yankees had a record 30 players on the IL this season, yet still managed to win 103 games along with the AL East, mostly without Stanton. So it’s not like losing him now is any reason to panic.

The nature of the strain, however, is a little confusing. Boone said Stanton first hurt himself legging out an infield single in the second inning, but he remained in the game and hammered a 406-foot homer in the sixth. Stanton also made a running catch in leftfield before he was removed later in the eighth inning for Cameron Maybin.

Getting replaced by Maybin was not all that unusual for defensive purposes, and Brian Cashman said he didn’t even know Stanton was hurting until the trainer called him over in the clubhouse after the Yankees’ 7-0 win. Beyond that, Boone said before Game 2 that Stanton still was available “in an emergency situation” off the bench, but preferred to stay away from him in the hope his leg could improve with the day off Monday.

The Yankees have good reason to be cautious. If Stanton is removed from the ALCS roster with an injury, he then becomes ineligible for the next round, the World Series. At least with Maybin and Aaron Hicks on the roster, they can carry Stanton in the hope that a few days rest can make him a functioning player again.

But with the team’s murky diagnosis, it’s tough to determine the severity of Stanton’s injury, or his chances of returning for Tuesday’s Game 3. We also can’t tell if it’s a somewhat positive sign that this is a new affliction rather than an aggravation of his other ailments, which included a torn left biceps, a sprained left shoulder, a calf issue and a sprained right knee.

Presumably, it was the lingering knee problem that prevented Stanton from returning until Sept. 18, and he was able to cram in only 34 plate appearances, along with five starts in leftfield, to get up to speed for the playoffs. Stanton has looked rusty, but he drilled his first homer of this postseason on the very same night that he suffered the injury.

The Yankees had been on an almost unprecedented stretch of good health, nearly two weeks without anything cracking, tearing or rupturing. We’ve been asking Boone since April whether the Yankees would ever reach a breaking point on the injury front, and he’s not about to make any such concessions now.

“No, that point hasn’t hit yet,” Boone said. “Absolutely not. And especially where we are now, where we are a lot more whole than we’ve been. So we’re obviously disappointed because we feel like G’s really gaining some steam and having good at-bats and we know what kind of impact player he could be. But we know when we turn to Cam or Aaron in this situation, we know what they can be.”

But do they? The Yankees like Maybin’s defensive ability in leftfield, and he homered in the ALDS Game 3 clincher, but they must be very skeptical about Hicks’ readiness not to go with him instead. Cashman gave Hicks $70 million back in March, but they don’t have enough faith in his current condition for him to fill in for Stanton’s sudden absence.

“Tough call,” Boone said. “Obviously [Justin] Verlander is a tough matchup either way. Just felt like with Aaron not having played obviously in a game yet, it’s a tough first-game draw.”

And with Hicks having even less preparation for this than Stanton got over the second half of September, who knows what could go wrong? Cashman suggested that Stanton’s rush back for October could have contributed to the quad injury.

“His return-to-play protocols were truncated,” Cashman said. “And that’s always been a worry of ours because of that. But this time of year, you’ve got to do what you’ve got to do to make sure that you can put him in the lineup.”

And for Sunday’s Game 2, Stanton was missing again. Nothing new for the Yankees, who by now should know how to win without him.