"So once we get him facing some hitters," Melvin said, "then we can plot a course."
Mengden fractured a bone below his right big toe while throwing a bullpen session at his home in Houston on Jan. 31, leading to the Feb. 8 procedure and a six-week stretch in a walking boot.
The injury was especially untimely for Mengden, who at the time of the incident was considered a top contender for a job in the A's rotation.
Oakland's starting staff has since been rocked by more injuries, but several pitchers, like Mengden, are on the mend: Kendall Graveman (shoulder) could return next week; Sonny Gray (lat) is expected back when the calendar turns to May; and Chris Bassitt (Tommy John surgery) is looking toward a June return.