Rafael Montero has not had a great month, and things took a turn for the worse on Saturday night.
The Mets' No. 2 prospect exited his start for Triple-A Las Vegas with an apparent injury to his left side after throwing only five pitches.
The 51s posted a 7-1 victory at Oklahoma City, but no information was immediately available regarding Montero's status.
The 23-year-old right-hander made four May starts in the big leagues, going 0-2 with a 5.40 ERA. Since returning to the Pacific Coast League on June 3, he's given up nine runs -- four earned -- on 13 hits and six walks over 8 2/3 innings in three starts.
Montero (4-2) got RedHawks leadoff hitter Austin Wates to fly to center field on a 1-2 pitch, then threw two strikes to Enrique Hernandez before he required the attention of 51s trainer Joe Golia.
Travis d'Arnaud, who played in 39 games for New York before returning to Las Vegas on June 9, homered for the second consecutive night and has four long balls in a four-game span. He's batting .417 in six Triple-A games.
Las Vegas endured another early loss of a starting pitcher on June 5, when Noah Syndergaard recorded two outs before injuring his non-pitching shoulder while covering home plate. Syndergaard, MLB.com's No. 10 overall prospect, has not pitched since and remains on the seven-day disabled list.