Seattle Mariners first baseman Ji-Man Choi has been suspended for 50 games following a positive test for a performance-enhancing substance.

The urine sample was collected from Choi before March 28, when Major League Baseball and the players' union increased the penalty for some violations. Choi is the third MLB player suspended this year.

Choi is considered a prime prospect for the Mariners, as he hit .295 last year and 18 homers, plus a .512 slugging percentage.  He had started the season with AAA Tacoma, and was expected to be called up from the Raniers to the big league club later this season.