June 21 (UPI) -- Oakland Athletics starting pitcher Frankie Montas was suspended 80 games after testing positive for Ostarine, a banned performance-enhancing substance, the MLB announced Friday.
Montas' 80-game suspension is effective immediately and makes him ineligible to pitch in the postseason. He can return to the A's near the end of the regular season in September.
"While I never intended to take any prohibited substance, I unfortunately and unknowingly ingested a contaminated supplement that I had purchased over the counter at a nutrition store here in the United States," Montas said in a statement. "That said, I respect MLB rules and understand my responsibilities under the Joint Drug Agreement, and accept full responsibility.
"I sincerely apologize to the A's organization, the fans, my teammates, and my family for this mistake. My hope is to be able to return to the A's later this season and contribute as best I can."
Montas has had a breakout season with the A's and was considered an All-Star candidate before his suspension. He had a 9-2 record with a 2.70 ERA and 97 strikeouts against 21 walks in 90 innings this season.
The Athletics (40-36) are one game behind the Boston Red Sox for the second wild-card spot in the American League.
"The A's were disappointed upon learning of this suspension," the club said in a statement. "We fully support MLB's Joint Drug Prevention and Treatment Program and we will welcome Frankie back after the discipline has been served."
Before his suspension, Montas tossed eight strong innings against the Tampa Bay Rays on Thursday. He gave up only four hits and one earned run and recorded nine strikeouts.
The pitcher opted against appealing the suspension and will serve the first-time penalty, according to ESPN.