The team said Wednesday on Twitter that he will be examined by Dr. James Andrews.
De Leon, 25, is the Rays' second top prospect to incur a major elbow injury this spring training. Right-hander Brent Honeywell, the MVP of last year's All-Star Futures Game, was hurt pitching batting practice on Feb. 22. Honeywell tweeted on Feb. 28 that he had undergone Tommy John surgery with Andrews.
De Leon made his big league debut with the Los Angeles Dodgers in 2016 and was 2-0 with a 6.35 ERA in four starts. Acquired the following January by the Rays, he pitched in one game for Tampa Bay last season, winning at the Texas Rangers on May 29, when he allowed three runs in 2⅔ innings and on 69 pitches -- the most by a Rays reliever since Chris Archer in September 2012.
De Leon made 10 minor league appearances last season and spent three stints on the disabled list due to discomfort in the flexor mass muscle, a strained lat muscle and forearm tendinitis, and back tightness. He had a pair of one-inning appearances in spring training this year, on Feb. 26 and on Saturday.