BOSTON — The Yankees’ pitching took another hit on Sunday, when CC Sabathia was placed on the 10-day injured list with right knee inflammation.

Sabathia was coming off a second straight subpar performance in Saturday’s loss to the Red Sox, when he gave up five runs — all earned — in just 4 ¹/₃ innings, as the Yankees’ rotation delivered a seventh consecutive poor start.

Aaron Boone said the decision to place Sabathia on the IL was made after Saturday night’s game, adding the left-hander’s surgically repaired right knee has “been a little cranky lately.”

Sabathia was asked about the state of his knee following Saturday’s outing and said: “I am not making excuses. I am out there and am expected to get outs.”

This is Sabathia’s second trip this season to the IL because of his knee.

He was also out in late May with a similar issue, but Boone made no guarantees the lefty would be back in 10-14 days, as he sometimes is when his knee bothers him.

“We will see,’’ Boone said on Sunday before the Yankees looked to avoid a series sweep to the Red Sox at Fenway Park. “I don’t want to speculate on that. We will see how these days unfold right now and see where he is at.’’

Sabathia is expected to get injections in his knee and the timing of those would impact when he could return.

“I would say I am not as clear on that,’’ Boone said. “I wouldn’t even say I am not optimistic. I am not sure exactly what it is going to be right now, whereas the last time, just the timing with the injections he gets we knew what it was going to be.’’

In what he has said will be his final season, Sabathia has been inconsistent, but pitched well in four straight starts leading up to his previous outing in Minnesota.

Combined with Saturday’s game against the Red Sox, Sabathia has allowed 12 runs — 11 earned — in just 8 ¹/₃ innings over the two games.

Boone said it was “possible” that Sabathia’s knee was the cause for his performance on Saturday.

“It’s always something that affects him,” the manager said. “It’s partly why he is a different pitcher [than earlier in his career]. The knee is a real issue for him.”

But the 39-year-old is hardly alone in his struggles, as every member of the rotation has failed to deliver over the last week — including James Paxton in his past two outings.

Pitching coach Larry Rothschild said after Saturday’s loss that it was up to him to straighten out the rotation, but it’s clear each pitcher is struggling with different issues.

The Yankees, who called up Tyler Wade from Triple-A Scranton/Wilkes-Barre, turned to Domingo German on Sunday.

With this week’s trade deadline approaching, GM Brian Cashman has already been scouring the market for help and Sabathia’s injury — while not particularly surprising, considering his history of knee problems— doesn’t help.

As for Sabathia’s spot in the rotation, the Yankees could have another starting pitcher by the time his turn comes up again. Boone said J.A. Happ will start on Tuesday against the Diamondbacks when the Yankees return home, followed by Masahiro Tanaka on Wednesday.

If they don’t add a starter, they could also use an opener again, as they have at different points of the season to much success, with Chad Green pitching well in the role.