CLEVELAND -- Dellin Betances' rehab from a spring training shoulder injury appears to have hit a snag, as the New York Yankees reliever will be undergoing testing Monday to determine the extent of the soreness he felt following a recent workout session.

Originally, the soreness had been believed to be "normal," according to manager Aaron Boone.

It was after facing hitters Wednesday in the first live pitching outing of his rehab from a right shoulder impingement injury that Betances felt some discomfort. He reported that feeling Thursday but believed it would dissipate.

By Friday, when Betances was scheduled to throw a side session off a mound at the Yankees' facility in Tampa, Florida, it had not.

"He got out and started long toss and got on the mound and felt like it was still there," Boone told reporters Saturday in Cleveland. "He backed off, and I thought that was wise."

Boone said Betances was tested Friday and that he saw an orthopedist at the team's spring-training complex. Although the testing went well, according to Boone, the Yankees are having Betances fly back to New York this weekend so he can be evaluated further Monday by team physician Dr. Chris Ahmad.

"Hoping it's not serious, but we'll know a little more in a couple days," Boone said.

The manager described the pain as being in Betances' back, around his lat muscle. Starter Luis Severino, who also has been out since spring training, is currently rehabbing from a right lat strain himself.

Betances first felt some slight discomfort in his shoulder during spring training. At that time, his velocity was noticeably down. Normally operating in the upper 90s, his fastball was hovering closer to 90 mph. Delayed arriving to spring training by a week due to the birth of his first child, Betances thought he was just easing into form a little more slowly than normal. But an MRI ultimately revealed an injury.

He's been shut down and subsequently rehabbing since then, being administered a cortisone shot as part of his recovery. Betances had reported feeling stronger in throwing sessions he had at Yankee Stadium last week as he anticipated the next stage of his return: facing live hitters.

Without Betances, Yankees relievers entered Saturday's game in Cleveland with a 3.76 ERA, the fifth-lowest in the majors. Their 10.21 strikeouts per nine innings are also the third-best mark in the league.

"He's Dellin Betances. It just lengthens your bullpen [having him]," Boone said. "He's a great pitcher, and hopefully this is just something that slows him a little bit. He's obviously a very important player to what we do.

"No denying how important he is to our club."

There's also little denying the impact All-Stars Giancarlo Stanton and Aaron Judge have on the Yankees. Both injured sluggers are still on the mend from respective calf strain and oblique strain injuries. Stanton could be a little more than a week away from coming off the injured list, while Judge remains slightly further away from returning.

Both players are going through rehab at the Yankees' facility in Tampa.

Boone said Saturday that Stanton will be starting a rehab assignment with the High-A Tampa Tarpons on Monday or Tuesday. It'll be his second rehab stint with them, after he was sent back to the IL due to complications after a pitch hit him on his left leg in an extended spring training game a few days prior.

After a few games with the Tarpons, Stanton will be moved to Triple-A Scranton/Wilkes-Barre to finish his rehab stint. The assignment spread across the two teams is expected to last "at least a week," Boone said.

Judge could begin his own rehab assignment in the next two weeks, Boone said. Earlier this week, he said Judge could possibly return by the time the Yankees travel to London later this month to face the Boston Red Sox.

One Yankees infielder who might miss out on that trip is Troy Tulowitzki. The 34-year-old shortstop who has been rehabbing from his own left calf strain since the beginning of April has paused his rehab for a few days to travel home to Southern California from the Yankees' Florida facility.

"He's kind of just trying to weigh everything that's going on with our organization, where he's at," Boone said Saturday, speaking extensively about Tulowitzki's absence for the first time. "Obviously it's been a tough time for him battling back and getting back and having a setback and everything. So he's just taking some time to go through things with him and his family and his agent. So we'll respect that time."

Tulowitzki, who hadn't played a game since 2017 entering this season due to ankle and heel injuries, is hitting .182 with a double and a home run in five games this season. As the Yankees have become deeper organizationally with Didi Gregorius' return from the IL this weekend, there may not be a place for Tulowitzki on the Yankees' roster.