The 25-year-old left-hander pitched four innings in a rehab start for Triple-A Nashville on Tuesday, throwing 72 pitches, allowing one earned run on four hits and striking out five.
"He felt great, granted it was four-plus [innings]," Melvin said. "As long as the pitch count was in the neighborhood of 70-75, which it was, we can kick him up into the 90 range [Monday]."
Manaea is 1-2 with a 5.18 ERA in five starts for Oakland this season with 27 strikeouts in 24 1/3 innings. The southpaw started 24 games for the A's as a rookie in 2016, going 7-9 with a 3.86 ERA.
Dave Sessions is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.