OAKLAND, Calif. — A season full of All-Star potential for Oakland Athletics pitcher Frankie Montas was drastically cut short Friday when Major League Baseball suspended him 80 games after testing positive for a performance-enhancing substance.

Montas pitched well Thursday night and is 9-2 with a 2.70 ERA in 15 starts, a big reason the A's are 40-36.

The 26-year-old righty could return for the final week of the season. But the penalty makes him ineligible for the All-Star Game and post-season play this year, and he'll lose about half of his $560,000 salary.

"I think it was a shock to everybody," A's manager Bob Melvin said before a night game against Tampa Bay. "We met as a team and Frankie spoke and was very remorseful and is going to accept what he has to deal with and feels bad about it."

The commissioner's office said Montas tested positive for Ostarine, a PED. He is the sixth player suspended this year under the major league drug program.

"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 released by the players' union.

Montas said he accepted "full responsibility" for the penalty.

"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," he said.

Montas pitched eight innings of one-run ball Thursday night. He got a no-decision in a game Oakland won 5-4 over Tampa Bay.

Montas allowed four hits, struck out nine and walked none. He struck out at least nine for the third straight start.

In a statement, the A's said they will "welcome Frankie back after the discipline has been served."

"Unfortunately it was a guy that everybody is pretty close to here and a guy that's performed really well. It's just something we're going to have to deal with," Melvin said.

Montas spoke to general manager David Forst at the Coliseum earlier in the day.

"I met with him this morning when he got to the ballpark. He was very disappointed in himself. He was apologetic. He feels like he let his teammates and the organization down," Forst said.

"I appreciated that sentiment but at that point there wasn't much we could do. I just think he wanted to express his remorse. After he talked to me, he met with Bob in private and talked to him," he said.

Forst said Montas had known about the positive test "for a while."

"It's disappointing on a number of levels. Obviously personally disappointed in Frankie," Forst said. "Disappointed for his teammates and for this team who have worked very hard the first half of the season, played very well of late and I know have high expectations of themselves going forward. It's disappointing."

The A's recalled right-hander J.B. Wendelken from Triple-A Las Vegas. The 26-year-old was on Oakland's opening day roster and is 0-1 with a 5.57 ERA in 18 games during his first season in the majors.