(Reuters) - The San Francisco Giants' pursuit of a deep run into the postseason suffered a jolt Wednesday when All-Star outfielder Melky Cabrera was suspended for 50 games without pay after testing positive for testosterone.

The 28-year-old from the Dominican Republic, the most valuable player in this year's All-Star game, was hit with the ban for violating MLB's drug prevention and treatment program.

Cabrera's suspension is effective immediately, the baseball commissioner's office said Wednesday in a statement.

"My positive test was the result of my use of a substance I should not have used," Cabrera, who will become a free agent after this season, said in a statement.

"I accept my suspension under the joint drug program and I will try to move on with my life.

"I am deeply sorry for my mistake and I apologize to my teammates, to the San Francisco Giants organization and to the fans for letting them down."

The eight-year big-league veteran is batting .346 -- second in the National League -- with 11 home runs, 84 runs scored and 60 runs batted in this season.

San Francisco is tied with the Los Angeles Dodgers for first place in the National League West with a 64-53 record.

The Giants have only 45 games left in the regular season, so Cabrera's suspension would stretch into the playoffs should San Francisco advance.

(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Steve Ginsburg)