BOSTON — Not every rough outing by a starting pitcher is cause for concern, especially when that pitcher has been as steady as Domingo German.

But it’s also true the right-hander is in uncharted waters.

German entered Friday having already thrown a career-high 132 ¹/₃ innings and a potential limit has been discussed since almost the beginning of the season.

That talk could continue after a 6-1 loss to the Red Sox at Fenway Park to start a season-long 10-game road trip.

German, coming off two good starts in which he had given up just three runs over 11 innings, didn’t allow a hit through the first three innings on Friday.

But he was done in by a four-run fourth.

Aaron Boone, nevertheless, is confident the bad night was just that — and not a result of German’s workload over the season. The manager said there are no current plans to skip a start or otherwise cut back his innings.

“I still feel like he’s physically sound,’’ Boone said. “If and when we get more guys in mix that might happen. I’m not in a rush right now to give him a break. I think he’s thriving in his routine. We’ll continue to watch him closely. We may alter some things, but not right now.”

The Yankees could get Luis Severino or CC Sabathia back before the end of the month, which could give Boone more options, but German agreed with his manager and said he was fine.

“I feel strong,’’ German said through an interpreter. “Every inning I go out there, I feel like I’m getting stronger and my body is getting used to it. There’s no need for me to skip a start or get extra rest.”

A lack of command on his curveball was German’s undoing, and he was hurt by it in the fourth.

Rafael Devers delivered Boston’s first hit of the game, a double off the Green Monster to lead off the inning.

German struck out Xander Bogaerts and J.D. Martinez grounded to second, moving Devers to third. Following an Andrew Benintendi walk, Brock Holt drilled a hard grounder that got by Gleyber Torres at second for an RBI single to give Boston a 1-0 lead.

Mitch Moreland then sent a three-run shot into the seats in right to make it 4-0.

German left after allowing five runs, all earned, in just 4 ¹/₃ innings. He also walked four.

Meanwhile, a trio of Boston pitchers retired the first 11 Yankees batters of the night until Didi Gregorius laced a double down the left-field line off Marcus Walden with two outs in the fourth. Gary Sanchez followed with a walk, but Edwin Encarnacion whiffed to end the inning.

Brett Gardner got the Yankees on the board with a homer off Andrew Cashner in the fifth, but that was it. The seven Red Sox pitchers shut down the Yankees, taking advantage of the expanded rosters.

“They did a good job of getting ahead,’’ Gardner said. “We couldn’t get anything going.”

Gardner knows the Yankees will see more teams use plenty of pitchers against them the rest of the regular season.

“That’s September baseball, unfortunately,’’ he said. “We’ve got three more weeks of that. Our job is to go out there and score runs, regardless of who we’re facing.”

Nestor Cortes Jr. came in and gave up a two-run double to Bogaerts after German left a runner on in the fifth. That bloated German’s road ERA to 5.73, compared to 2.35 at Yankee Stadium.

Both Boone and German dismissed any possible importance to the split, but it’s something to watch.

No starter has been more consistent for the Yankees than German, but he still has more to prove.