ST. PETERSBURG -- Right-hander Daniel Gossett, the Athletics' No. 5-overall prospect according to MLBPipeline.com, will make his Major League debut on Wednesday against Miami.
Oakland manager Bob Melvin announced the decision before Sunday's finale against the Rays. Righty Jharel Cotton will open the two-game set at Marlins Park on Tuesday.
A 2014 second-round pick out of Clemson University, Gossett is 3-3 with a 3.41 ERA in 11 starts for Triple-A Nashville this season. He was named the organization's pitching prospect of the year by MLBPipeline in 2016.
"I've said many times, you'd like to get a guy here when he's pitching well for his debut, and he has been," Melvin said. "So I think the timing is good for that."
Having not pitched since Monday, Gossett will come into the start on more than a week's rest. To get him ready, Melvin said the 24-year-old was scheduled to throw a "significant" side session on Sunday before he joins the team following the off-day on Monday.
Melvin said Gossett's potential jumped out at him during Spring Training, during which he appeared in three games, walking six and striking out one to finish with a 4.26 ERA.
"You know what, he's got a quick arm -- there's some deception," Melvin said. "He's got a really good cutter, he's got a good changeup, he's got a good mix of pitches and he's got some presence out there on the mound, too.
"I wouldn't say he knows he's good, but he probably does."
• The A's optioned struggling reliever Frankie Montas to Triple-A Nashville before the game. The right-hander (1-1, 6.91 ERA) has dealt with trouble finding his groove through 21 appearances this season, allowing nine home runs with 15 walks.
"He's going to be a monster in this league. I believe that," Melvin said. "He just wasn't able to get out of what was a little bit of a rut, and confidence-wise, he's a tough kid. I never really saw the guy deer-in-headlights. … When you have several outings like that, maybe a reset button is a little bit better for him."
• Melvin said righty Kendall Graveman (shoulder) was scheduled to play catch on Sunday. Shortstop Marcus Semien, (wrist surgery), has advanced to hitting soft-toss.