Seattle Mariners prospect Choi Ji-man has been suspended for 50 games after the first baseman tested positive for a performance-enhancing drug, Major League Baseball said on Thursday.


South Korean Choi was on the Mariners' 40-man roster and was hitting .394 with one home run and five RBIs in 10 games for the Mariners' Triple-A affiliate Tacoma this season.


The 22-year-old, who signed with the Mariners in 2009, tested positive for methandienone and his suspension was effective immediately, MLB said.


"I do not know what I could have taken that caused me to test positive," Choi said in a statement. "I have not and never would knowingly use anything illegal to enhance my performance.


"However, I also understand that without an explanation I must serve a suspension and I accept that."


The Mariners said they were "disappointed" with Choi's suspension but supported MLB's efforts to eradicate doping from the game.