"Physically, he's fine," Melvin said. "It's just about getting him enough pitches to where he can start in a game again."
Gray threw a three-inning simulated game at the Coliseum on Tuesday, tossing 50 pitches and facing batters for the first time since going on the DL on May 22. The right-hander was pleased with the results, saying it felt "free, nice and easy."
"I feel like my stuff, just talking to the hitters, it seemed to be coming out really well, just late life, which is kind of trying to get back to where I want to be," Gray said.
Gray has focused on mechanical adjustments throughout much of 2016 and said they felt more comfortable on Tuesday. Melvin said Gray will benefit from appearing in a game environment.
"You have to create your own intensity for simulated games," Melvin said. "When you're in a real game, it's a little bit different scenario."
• Melvin also said lefty Rich Hill, who has anchored the top of the A's rotation for much of this season, will start on Saturday against the Astros. Hill left his start on Sunday against the Tigers with a groin strain, but he threw a clean bullpen session on Tuesday.
The A's have an off-day on Thursday, so Hill will pitch on six days' rest. The 36-year-old is 8-3 with a 2.25 ERA in 11 starts this season, and he has posted a 3.03 ERA in 14 career starts on six or more days of rest.
• Melvin said Henderson Alvarez (shoulder) will throw a bullpen session this weekend.
"If all goes well there, maybe we'll do something either simulated or a rehab for him," Melvin said.
• Liam Hendriks (triceps) will throw a simulated game with Stockton either Saturday or Sunday, according to Melvin.
Mark Chiarelli is a reporter for MLB.com based in Oakland. This story was not subject to the approval of Major League Baseball or its clubs.