Joey Gallo could be in his final days as a Yankee, and if he is, he’s going down largely out of sight.

The struggling outfielder was not in the Yankees’ starting lineup Wednesday for the third time in their last four games and the sixth time in their last nine. Then, after the Yankees’ 3-2 loss to the Mets, they traded for left-handed hitting outfielder Andrew Benintendi from the Royals, further clouding Gallo’s future in The Bronx.

Gallo did not start in either of the Subway Series games against the Mets, but after he struck out as a pinch hitter against Edwin Diaz in Tuesday’s loss, manager Aaron Boone left him on the bench for a potential pinch-hit spot in the ninth inning of a tie game Wednesday. Instead of pinch-hitting Gallo for Kyle Higashioka against Mets right-hander Seth Lugo, Boone went to the right-handed hitting Jose Trevino, who struck out.

“Lugo’s much more of a neutral guy,” Boone said. “I wanted Trevy in that spot.”

Boone, who said before Wednesday’s game that he expected Gallo to “probably” be back in the lineup on Thursday against the Royals, went to bat again for his struggling outfielder.

“Look, I think it’s been tough for Joey, there’s no question about it,” Boone said. “It’s been a tough road for him since coming over here where he just kind of hasn’t found that traction. There’s no question in my mind that there’s still great baseball ahead for him, whether that’s immediately or in the years to come, and that he is really talented and really cares and works.”

This season, Gallo is batting .161 with an 80 OPS-plus (20 percent below league average), 40 walks and 103 strikeouts in 80 games.

In 138 games as a Yankee, Gallo was batting .160 with 25 home runs, an 86 OPS-plus, 77 walks and 191 strikeouts. Nearly a full year since coming over in a trade from the Rangers — Friday will mark the one-year anniversary of the deal — Gallo could be on the way out before Tuesday’s trade deadline, especially with Benintendi on the way in.

“I think he’s born the brunt of struggling here a little bit,” said Boone, who also cited some mechanical work that hasn’t yet clicked for Gallo. “I think he’s worn that and carried that burden. As human beings, you want to do well and perform.

“As I try to remind him every now and then, though, he has all the equipment to still be great at this. He’s at an age (28) where he can still be great at this. Reggie Jackson used to always say to me, ‘You own the pen.’ He still gets to write the final script or add to the story. As long as you have the talent like he has, there’s that chance it can happen.”

Asked how much of that might be about Gallo not being a good fit for New York, Boone said he didn’t know.

“I just know it’s been a struggle,” Boone said. “I feel like it has weighed on him and he’s carried that around.”