Dellin Betances says he felt he owed it to his teammates to get an MRI today and get his shoulder injury fixed. (0:54)

TAMPA, Fla. -- New York Yankees set-up man Dellin Betances will begin the season on the injured list with a right shoulder impingement (inflammation), according to general manager Brian Cashman.

The impingement was discovered when the Yankees administered an MRI on Betances' throwing shoulder Tuesday morning, after the pitcher complained about his arm feeling weak this spring and routinely lacking comfortable extension at the completion of his throwing motion.

Those complaints, coupled with seriously lacking velocity -- Betances, whose fastball normally touches 97-98 mph, peaked at 92 just once in an eight-pitch outing at the Phillies on Sunday -- convinced all parties the reliever needed to be tested.

"You evaluate what you see on the field. In his case, you're seeing the radar guns," Cashman said. "We know that he's had a history in the past of slow starting, but this was a little longer and more significant than we recall and all our historical information showed."

Betances will immediately begin a cycle of anti-inflammatories, and will be shut down for a few days. The 30-year-old righty believes it will be three to five days before he's able to resume a throwing program.

"I'm not too concerned, it was just more precautious," Betances said. "I feel a little better to be honest with you, because I get to take my time a little bit. I feel like with a week left in [spring training], it wasn't going to be fair to my teammates to go out there not having the stuff that I'm capable of having."

Manager Aaron Boone believes this time off will aid Betances.

"Hopefully this is kind of a timeout, get him strong, get him healthy and build him back up without rushing things," Boone said. "Hopefully it ends up being sooner rather than later, but not the end of the world to have him miss a little bit of time and to save some innings over the course of a long season, because we're obviously going to need him and count on him in a big way."

The Yankees believe Betances' lowered velocity and weakened arm are the product of him having a more abbreviated offseason throwing program than normal.

The pitcher admitted after Sunday's appearance -- one in which he struck out Bryce Harper with a rising, yet lukewarm 90 mph fastball -- that he took more time off at the start of the offseason than he normally does. He tried to replicate the timing he had last offseason, when he also began throwing a little later than normal.

Right when Yankees pitchers and catchers were arriving at spring training, though, Betances ended up with even more time off. His wife had just given birth to their first-born, causing Betances to spend an extra week at home with them.

Betances thinks because he was a little late to camp, he tried too hard to rush his arm along to regular-season strength.

"I felt like I was trying to rush to get back and compete," he said. "I'm just a little behind. But I'm not concerned at all."

Betances had a 2.70 ERA and struck out 115 over 66 2/3 innings last season while serving as the primary setup man for Yankees closer Aroldis Chapman.

According to ESPN Stats & Information, Betances also ranks third all-time in career strikeouts/nine innings pitched. His 14.6 strikeouts/nine is only behind Craig Kimbrel's 14.7 and Chapman's 15.0.

"Our expectation is we'll sooner than later, you'll see the Dellin that you're used to seeing rather than the Dellin that we've been seeing right now," Cashman said.

This is just the latest in a series of spring-training injuries for the Yankees. Center fielders Aaron Hicks and Estevan Florial have been banged up with this spring, with Florial looking at a long stay on the injured list with a broken wrist. Hicks also will begin the year on the IL, although that stay isn't expected to last very long.

Starting pitchers Luis Severino and CC Sabathia also will be on the IL into April. Severino is fighting through his own right shoulder inflammation, and Sabathia is returning from offseason knee and heart procedures.

"We're taking hits," Cashman said. "These are resolvable ones in that these have expiration timing tags to them. For that, you're thankful. You'd rather not be going through any of it, but when you are going through it, then you think, 'Well, things could be worse.'"

Boone said the Yankees have their share of pitchers who can fill Betances' shoes in the interim. Lefty Stephen Tarpley could be a prime candidate, Boone added. In 10 innings this spring, Tarpley, a 26-year-old pitcher who was called up late last season, has seven strikeouts and allowed just five hits and no runs.

"We feel like we have the depth that we're still going to go north with a dynamic bullpen," Boone said.