Kinney was a top candidate for setup relief pitcher this year. He first tore the ulnar collateral ligament in his pitching forearm one year ago.
Team physician Dr. George Paletta said Thursday the torn ligament has grown increasingly worse. The torn ligament in Kinney's right arm should be surgically replaced with a tendon from his left wrist, Paletta said. Kinney's recovery should take about 10 months.
After pitching three innings in a spring training game Monday, Kinney said he could not flex his arm fully. Kinney had an MRI on Tuesday, and Paletta diagnosed the injury Thursday.
"It just locked up on me after the game," Kinney said. "It stinks, because I was really looking forward to being a part of this clubhouse this year."
Cardinals manager Tony La Russa noted after Monday's performance that something seemed wrong with Kinney's pitching. Over a one-inning showing in each of two games, Kinney allowed six hits and six earned runs. He struck out no batters and walked two.
"We knew this was something where he'd be out six to eight weeks or need surgery," La Russa said.
Last season, Kinney pitched 25 innings in 21 games with a 3.24 ERA.