TAMPA, Fla. -- Luis Severino reached back for a few fastballs Tuesday, popping catcher Gary Sanchez's mitt without issue. Then he snapped off a slider, and the ensuing discomfort behind the hurler's right shoulder set off alarm bells in the Yankees' universe.

Severino immediately halted his warmup, alerting pitching coach Larry Rothschild that something was off. An MRI showed inflammation in Severino's right rotator cuff, and the right-hander will not throw for two weeks, which manager Aaron Boone said will make Severino "highly unlikely" to be ready for Opening Day.

"Better it happened now than during the season," Severino said on Wednesday morning. "I think it's something that we can treat now and move forward to the season and be able to pitch."

Severino, 25, had been scheduled to make his spring debut Tuesday against the Braves at George M. Steinbrenner Field, an exhibition that the Yankees won, 5-1. Severino said that it was the first time that he had experienced that type of discomfort, though he was not worried when he entered the MRI tube.

"I wasn't scared, because I knew it was nothing bad," Severino said. "It wasn't anything about my shoulder, what was happening was something about my muscles. I knew it was going to be nothing bad."

Attended to by team physicians Dr. Christopher Ahmad and Dr. Daniel Murphy, Severino received a cortisone injection on Wednesday and is expected to be re-evaluated in two weeks.

"He's an important piece and we're not going to have him for a period of time," general manager Brian Cashman said. "We'll adjust, because that's what everyone has to do, but it's a concerning situation until he's on the mound for a consistent period of time to the point that you forget that it ever happened. We're a long way from that."

"They want to keep me healthy," Severino said. "I feel like I'm going to get better before that. That's going to be my routine now. I can't play catch for two weeks. Then after that, I think I'll play catch, maybe 90 [feet] or something like that."

Severino was the Yankees' probable starter for the March 28 season opener against the Orioles, but those honors could now go to right-hander Masahiro Tanaka or left-hander James Paxton. Boone said that the decision had not yet been made.

Though Cashman said that the Yankees remain open to opportunities that make sense within their parameters, he added that the club is prepared to fill Severino's vacancy from within. The most likely internal candidates are Domingo Germán or Jonathan Loaisiga, a pair of right-handers who have impressed in the early going this spring.

"What I've got is what I've got," Cashman said. "We're comfortable with that, but we also recognize that as the season plays out, we're going to have to add to this group regardless. More realistic additions will come after the Draft [in June]. You never know. I can't rule anything out, but I'd say the main focus is what we have."

An All-Star in each of the last two seasons, Severino believes that he will recapture that form when healthy, but he said that it will be difficult waiting to be cleared for action.

"This is the game that I love and I want to be there for the first game, so it's going to be tough for a little bit," Severino said. "But like I said, it's better to happen now than in midseason or at the end of the season. God has a plan for everybody."