"Our guys are telling us that he's really pitching well and he's come a long way," Melvin said after the A's beat the Angels, 5-4, at Angel Stadium. "He's got a complement of pitches that gets him through righties and lefties both. We were impressed with what he did this spring. He's just continued to develop."
The A's have had only four healthy starters since Sean Manaea went on the disabled list June 14 with an elbow strain, resulting in a need for more arms.
"We're at a point now where not only have we had some injuries and we've been using some guys, this is a guy that we like," Melvin said. "He's healthy finally now and pitching well and you like to get a guy here when he's pitching well."
The A's will need to make a move to free up space for Overton on the 40-man roster.
Left-hander Eric Surkamp will start on regular rest Friday instead of on his previously scheduled turn Saturday.
• Henderson Alvarez, who was recently shut down in his rehab from right shoulder surgery, visited with Dr. James Andrews on Wednesday and Thursday. Andrews performed Alvarez's shoulder surgery last July.
"We still don't have a determination on where we're going yet," Melvin said. "I think they're just trying to figure out what's going on in there. He feels reasonably good again. So it's kind of a confusing situation. They're trying to get to the bottom of it before he leaves."
Alvarez reported discomfort in his shoulder during his most recent rehab start with Triple-A on Saturday. Before the setback, that was thought to be the final rehab outing for Alvarez before the veteran joined the A's. The 26-year-old has yet to debut with Oakland after signing a one-year, $4.25 million deal in the offseason.
Austin Laymance is a reporter for MLB.com based in Los Angeles. This story was not subject to the approval of Major League Baseball or its clubs.