TAMPA, Fla. -- Luis Severino is "highly unlikely" to be ready for Opening Day, according to manager Aaron Boone, who said the Yankees' ace will not be permitted to throw for at least two weeks due to right shoulder inflammation.

Severino was scheduled to make his spring debut on Tuesday, but the right-hander reported discomfort behind his pitching shoulder after snapping off a slider during warmups. Severino underwent an MRI and will receive a cortisone injection and anti-inflammatories before resuming a throwing program.

"Anytime a guy like Sevy walks off when he's warming up to start a game, you always get worried and concerned about that," Boone said after the Yanks' 5-1 Grapefruit League victory over the Braves. "It sounds like the shoulder is pretty clean; it's just an inflammation issue. If that's the case, then hopefully two weeks is something that will do the trick."

The 25-year-old Severino, an All-Star the past two years, had been announced as the Yankees' probable starter for the March 28 opener against the Orioles at Yankee Stadium. Instead, right-hander Masahiro Tanaka or left-hander James Paxton appear likely to take those honors, though Boone said the club had not yet discussed the assignment.

"Obviously, it's a bummer," said left-hander J.A. Happ, who allowed one run over three innings of relief on Tuesday. "It's your guy that you were probably assuming was going to get the ball in Game 1 to start the season."

Tuesday's outing was to be Severino's first game action since he signed a four-year, $40 million contract extension on Feb. 15, though he did face Giancarlo Stanton and Gary Sánchez in a 39-pitch simulated game on Thursday. Left-hander Stephen Tarpley started instead, working a scoreless inning.

"It's 15 minutes before the game, so it's a little chaotic," Boone said. "You could see everyone was concerned. It's no secret how important he is to our team."

Severino was 19-8 with a 3.39 ERA in 32 starts last season, ranking third in the Majors in victories while finishing eighth in the American League with 220 strikeouts. His performance dropped precipitously in the second half, when he went 5-6 with a 5.69 ERA in his final 13 regular-season starts after beginning the year 14-2 with a 2.12 ERA in 19 starts.

Yankees team physicians Dr. Christopher Ahmad and Dr. Daniel Murphy examined Severino, who will be re-evaluated in two weeks.

Boone said he believes the Yanks have enough depth to weather the loss of Severino, stating that Domingo Germán and Jonathan Loaisiga are the most likely candidates to step into the rotation. Boone said both hurlers have been impressive, as have bullpen candidates Luis Cessa and Tommy Kahnle.

"We'll be covered," Boone said. "We feel like the guys that you would consider our sixth and seventh starters, we feel like we're in good shape there. The guys you'd consider filling out or competing for the back end of our bullpen and starting rotation, all guys have come in looking really well."

The club is also believed to have internally discussed free-agent left-hander Gio Gonzalez. To date, Dallas Keuchel has not been connected to the Yankees, though that could change if Severino's injury is deemed to be serious.

"I think you just kind of go next in line," Happ said. "That's part of baseball. I think you try to pick up the slack. Good teams are able to do that. But that's certainly a blow [with Severino], because that's a guy that you pencil in to really be effective for us. Hopefully it's not serious and it's just a matter of a couple of weeks. That would be best-case [scenario], I think."

It has been a rough week for the team's newest contract signees. Outfielder Aaron Hicks agreed to a seven-year, $70 million extension on Feb. 25, and he has not played since Friday due to ongoing back soreness.

Hicks said on Tuesday that he expects it will be a few more days before he returns to action, and the switch-hitting center fielder is hopeful that Severino will be able to enjoy a speedy recovery.

"It's a huge blow," Hicks said. "He's one of our better pitchers and we need him on the field. We'd rather this happen early and have him be able to finish the rest of the season strong."