OAKLAND, Calif. — Oakland pitcher Bartolo Colon has been suspended for 50 games after testing positive for testosterone, Major League Baseball announced Wednesday.

Colon, 10-9 with a 3.43 earned-run average, was a veteran presence on a team full of young talent that has become an unexpected AL West contender.

"I apologize to the fans, to my teammates and to the Oakland A's," Colon said in a statement. "I accept responsibility for my actions and I will serve my suspension as required by the joint drug program."

Tyson Ross will start in Colon's spot on Thursday against the Tampa Bay Rays.

"It's disappointing," general manager Billy Beane said. "From a baseball standpoint, we're scrambling. Bartolo was scheduled to start tomorrow in Tampa, and the obvious thought was a guy like (Dan) Straily, who we just sent down. But because of his option and the 10 days, he had to stay down."

Colon essentially is gone for the season. The Athletics began play on Wednesday with 40 games left in the regular season, so Colon can't be activated until the 11th game of the postseason, if the team makes the playoffs and gets that far.

Notes

• Johan Santana is done for the year, and to say he had an up-and-down season would be an understatement of Cy Young proportions.

Explaining that their ace is worn out from two years of rehabilitation and maintenance, the New York Mets placed Santana on the 15-day disabled list with inflammation in his lower back and said he is not expected to pitch again in 2012.

• Nationals manager Davey Johnson said Stephen Strasburg could miss his final two or three turns in the rotation during the regular season.