BOSTON — The Yankees are trying to figure out how to fix Masahiro Tanaka after another terrible outing against the Red Sox — the latest red flag in what has becoming a growing concern for the rotation.

So far they haven’t come to a conclusion, but according to pitching coach Larry Rothschild, the possible culprits include pitch-tipping, mechanics and lower seams on the baseballs this season.

The last one is what Rothschild believes, saying it has had an impact on Tanaka’s splitter.

“It’s the seams,” Rothschild said Friday at Fenway Park. “Overall, the baseball. I’ve thought that for quite a while.”

It’s given Tanaka “no margin for error,” according to Rothschild, and the Yankees have yet to find a solution.

“We have to find a grip that works,’’ Rothschild said before watching James Paxton get lit up in the Yankees’ 10-5 loss on Friday night. “We’ve looked for it, but he’s felt it’s been more mechanical than the baseball. We’re looking at both sides of it. He made some adjustments [Friday] and hopefully it’s gonna help.’’

Tanaka’s woes against the Red Sox have been especially pronounced. In his past two outings against the Yankees’ rivals, the right-hander allowed six runs in just two-thirds of an inning in London and then gave up 12 runs in just 3¹/₃ innings Thursday, leading the Yankees to look into potential pitch-tipping.

“If he had the splitter, I think it would have been different, but to what degree I don’t know,” Rothschild said of Tanaka’s recent issues versus Boston. “There’s clearly — whether he’s tipping or whatever else is going on — I don’t know right now. We need to figure it out.”

Aaron Boone said the Yankees “have a lot of eyes” on whether Tanaka is tipping pitches. There was thought that’s what led to Luis Severino’s disastrous outing in their lopsided loss to the Red Sox in Game 3 of the ALDS last season, when the right-hander allowed six runs in three-plus innings.

“Obviously, the Red Sox are very good at picking up any advantage you give them or seeing different things,” the manager said. “So it is something we try and stay on top of, obviously. We will continue to be all over that the best we can.’’