General manager John Coppolella announced before Saturday's game against the Pittsburgh Pirates that McKirahan is expected to miss the season after being diagnosed with a torn ulnar collateral ligament.
McKirahan will get a second opinion from Dr. James Andrews, but the Braves believe Tommy John surgery will be required. The 26-year-old pitcher already underwent that procedure in 2012.
"I really feel for the kid," Coppolella said. "This will be his second (Tommy John surgery). We thought he had a real shot to make the club this spring."
The injury occurred Wednesday on the fifth pitch of his spring debut against the Orioles.
"He felt fine," Coppolella said. "He actually threw some really good (bullpens). This is just part of it."
McKirahan missed 80 games last season after being suspended for testing positive for performance-enhancing drugs. He wound up pitching in 27 games, going 1-0 with a 5.93 ERA.
Pitching injuries have become such a part of the game, Coppolella said, that every team must plan for some sort of attrition during the season. The Braves have made a point to acquire as much pitching as possible while rebuilding their roster through myriad trades.
"That's why you keep getting pitching," the GM said. "Sign it, trade for it, because you just don't know."