"He impressed to the point where we could potentially use him in any situation," Melvin said Friday.
Those remarks come two days after Gray, Oakland's first-round pick in the 2011 First-Year Player Draft and ranked the organization's No. 5 prospect, struck out three and allowed just one hit over two innings of relief work against the Pirates in his debut.
"It didn't look like he was nervous about anything," Melvin said. "He threw all his pitches. Therefore, depending on a particular day and who's available, we're certainly not opposed to using him in a plus game and an important situation."
Gray was 8-5 with a Pacific Coast League-leading 2.81 ERA in 16 starts with the River Cats at the time of his promotion. His only other relief experience came in college and Spring Training, but the A's were confident in his readiness to contribute at the highest level in any role.
He'll remain in the bullpen at least through the start of the All-Star break and likely remain there after it concludes unless a rotation spot opens.
"We saw in Spring Training he's got a lot of energy and the command can be an issue when you're like that, especially in your first big league opportunity," Melvin said. "But he wasn't, and the command was really good. That was one thing we felt he needed to work on in the last couple of years, and he's done that. Very impressive kid. We'd use him in any particular role."
Jane Lee is a reporter for MLB.com. Read her blog, Major Lee-ague, and follow her on Twitter @JaneMLB. This story was not subject to the approval of Major League Baseball or its clubs.