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."
Worth noting • 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.
Jeff Odom is a contributor to MLB.com based in St. Petersburg.