TORONTO — One rehab start was enough for Luis Severino.

But the 22-year-old, looked at by many as an ace-in-waiting, won’t be returning to the Yankees’ rotation. At least not yet.

The Yankees returned Severino from the disabled list, where he had been since May 14 with a right triceps strain, and optioned the struggling righthander to Triple-A Scranton/Wilkes-Barre on Monday.

They hope Severino, 0-6 with a 7.46 ERA, can work through the difficulties that have plagued him from the start of the season.

“He’s healthy and we want to get him starting every fifth day and try to get him back on track,” Joe Girardi said. “It’s been a struggle for him this year. We need to get him going. He’s too talented to be pitching the way he’s pitched.”

Severino made a rehab start Sunday night for high Class A Tampa, allowing two hits and striking out two in three shutout innings.

The righthander was terrific last August after being called up and inserted into a pennant race, going 5-3 with a 2.89 ERA in 11 starts. He looked ready to build on that with solid and at times spectacular work in spring training but never got things going this season.

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“I think his command has to improve, locating his fastball better,” Girardi said, also mentioning Severino’s need to improve his off-speed pitches. “We want the next time he comes up to be a finished product.”

Girardi said it’s “not abnormal” for young players, especially pitchers, to have their ups and downs, using former Blue Jays and Phillies star Roy Halladay as an example.

“He was sent back down [early in his career],” Girardi said. “Figured it out and was pretty darn good once he came back up again. So this is just part of the process for young players.”

Ackley to DL; Refsnyder up

Dustin Ackley was put on the DL with a right labrum tear incurred Sunday when he dived back to first base. To take his place, the Yankees recalled fan-favorite utilityman Rob Refsnyder, who plays third, second and right but not first.

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Ackley had been Mark Teixeira’s primary backup, and with the first baseman just returning from neck spasms — and experiencing a laundry list of injuries in recent years — the Yankees are even thinner at first base, with the February loss of prospect Greg Bird looming even larger.

Nick Swisher and Chris Parmelee are options in the minors should something long-term happen to Teixeira, though the former isn’t moving well at all, according to scouts. A pickup from outside the organization can’t be ruled out.

As of now, catcher Austin Romine is Teixeira’s primary backup.

A-Rod gets a day

Alex Rodriguez, 1-for-16 with nine strikeouts since returning from the DL, was given Monday night off against Toronto righthander Marco Estrada.

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“I don’t make a ton out of [16] at-bats,” Girardi said. “He looked out of rhythm yesterday [A-Rod went 0-for-3 with two strikeouts Sunday). He hit a big home run Friday, but he hasn’t gotten on track yet.”