OAKLAND -- The tight-knit clubhouse atmosphere built this season by the A's was dealt a stunning blow Wednesday when Major League Baseball announced starting pitcher Bartolo Colon has been suspended for 50 games after testing positive for testosterone.

Colon, a 39-year-old right-hander who was 10-9 with a 3.43 ERA, was a veteran presence on a team full of young talent that has become an unexpected contender in the American League West.

But now Colon essentially is done for the year. He will miss the rest of the regular season and can't play again until the 11th game of the postseason, if the A's make the playoffs and get that far.

Colon apologized in a statement provided by the Major League Baseball Players Association.

"I apologize to the fans, to my teammates and to the Oakland A's. I accept responsibility for my actions, and I will serve my suspension as required by the Joint Drug Program," the statement said.

The suspension comes exactly a week after Giants outfielder Melky Cabrera tested positive for the same substance.

"It's disappointing," A's general manager Billy Beane said before the A's 5-1 win over the Minnesota Twins. "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."

Players optioned back to the minor leagues must stay there for 10 days before they can be recalled. The one exception is when another player is put on the disabled list. Straily was sent down Monday when Brett Anderson was activated and can't return until next week, when the A's are in Cleveland.

Beane met with the team before Wednesday's game, but many of the players already had learned of the news.

Colon was the A's leader in innings pitched with 1521/3 until he was surpassed by Tommy Milone on Wednesday. Milone went eight innings in gaining his 10th win against nine defeats.

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

Colon's suspension is the latest in a string of surprises for the A's, with catcher Kurt Suzuki being traded to Washington and second baseman Jemile Weeks being optioned to Triple-A Sacramento.

"He loosened up this clubhouse every day in some way or another," reliever Ryan Cook said of Colon, "but we've got all kinds of those guys. You look around, you name them. They're funny, they're loose. He was just another one. But we'll miss him, no doubt about it."

Other players talked about the impact stricter drug testing is having on the game.

"I know when I first got in the game, it felt like a thing people would think about and there might not be repercussions," pitcher Brandon McCarthy said. "Now it seems like, especially with the names that have come out, it's not nobodies that are getting busted. It's people that are bigger in the game and have a bigger presence. It seems like a stupid option, but it seems some people are still willing to do it for whatever benefit."

Added outfielder Josh Reddick: "Let's hope that guys are starting to realize this is a serious program. Nobody wants to be that person on TV."

Beane, who learned of the suspension Wednesday morning, said the team has depth when it comes to starting pitching. He said the team is more likely to rely on that depth than make a move to acquire a pitcher.

"The loss of any player hurts this time of year," Beane said. "It's been a pretty resilient group. We've had some injuries, and young guys in particular have picked up."

Manager Bob Melvin talked about the suspension before the game, saying his focus and the team's focus is to move on.

"We really do support the policy and obviously you're seeing people being caught, so it's obviously working," Melvin said. "As an organization, you have to sign players and have faith in what you're doing and there are some unknowns to it. Not just for us, I think that's any team."

It's not the first time Colon has been embroiled in controversy.

In May 2011, MLB launched an investigation amid reports he had received infusions of stem cells in the Dominican Republic in 2010.

Colon, who didn't pitch in 2010 and signed with the New York Yankees in January 2011, was sidelined with a torn rotator cuff and a damaged ligament in his elbow when he learned about stem cells from a local doctor, USA Today reported. He was subsequently cleared by MLB.