Now that the Yankees know they won’t be adding any significant arms for the rest of the season, the return of Luis Severino is even more critical.

And even the right-hander was caught off guard when the Yankees failed to make a move to boost their rotation or bullpen at Wednesday’s trade deadline.

“I think everybody was surprised there was no trade, but we have a good enough team to win in here already,’’ Severino said. “Dellin [Betances] is gonna be big, too.”

Both injured pitchers threw on flat ground again Friday in The Bronx before the Yankees opened their four-game series against the Red Sox with a 4-2 win.

Severino is expected to throw off a mound next Friday or Saturday in Toronto for the first time since suffering a strained lat when he was rehabbing from a shoulder injury that he got during spring training.

“It means I’m closer to coming back,’’ Severino said of the significant step he hopes to take next week. “I hope to be a big part of the team.’’

He’ll likely have to be if the Yankees expect to have much success in the postseason, given the inconsistency of the rotation.

General manager Brian Cashman made no secret of his pursuit of pitching over the past month and his failure to land an arm could prove costly in October. That’s why a healthy Severino — and to a lesser extent, a healthy Betances — will play such a vital role down the stretch.

Severino said he thinks he would throw about four bullpen sessions before moving on to live batting practice.

By then, the minor league season may be over, which means the Yankees would have to find a place for Severino to throw rehab games.

Austin Romine said he is confident Severino won’t take long to be back to his old self, as long as he remains healthy, since he typically is strong from the start of spring training and the regular season.

“He’s so good at what he does, normally it doesn’t take him long to get going,’’ Romine said. “He’s got such a good arm and is a great competitor, I think he’ll be fine, whenever he comes back. I know he’s itching to get here. We’ll see how it goes, but we know what he can bring to the table.”

Severino was upbeat after throwing Friday.

“I feel the best I have all year right now,’’ Severino said. “It’s been a great season for the team so far, and I want to be able to contribute soon. I feel like there’s enough time for me to do it.”