TAMPA, Fla. -- New York Yankees left-hander Zack Britton is not throwing because of a sore pitching elbow, was to be examined by a doctor on Tuesday and could miss the start of the season.

Yankees manager Aaron Boone said Britton's ulnar collateral ligament was not suspected of being hurt, which could require Tommy John surgery. Boone said Britton felt soreness Sunday night following a bullpen session and had an MRI of his elbow Monday.

"I would say it's always concerning any time any of your players are going through tests because they're not quite where we want them to be," Boone said. "But that said, let's find out where we're at and what it says and what the days ahead mean now. So Zack overall feels pretty good. He's in good spirits about it. But let's get the answers first."

Britton, 33, disclosed last weekend that he was recovering from COVID-19, which he contracted in January. He has not pitched in any exhibitions.

"I think [that] set him back a little bit in his buildup," Boone said. "Just trying to kind of get his weight up. He's actually been throwing pretty well early in spring."

Britton, a two-time All-Star, was 1-2 with a 1.89 ERA and eight saves in 20 appearances during the pandemic-shortened 2020 season. He filled in as closer when Aroldis Chapman was recovering from COVID-19.

Britton is entering his fourth full season with the Yankees and is starting the third season of a contract now worth $52 million over four years.