The Phillies have a crowded outfield, so it makes sense for the club to be patient with Mayberry and activate him once rosters expand on Monday. He's scheduled to return to Lehigh Valley for three more days, then join the Phillies for Monday's series opener in Atlanta, Sandberg said.
Mike Adams is also rehabbing with Lehigh Valley as he attempts to return from inflammation in his right shoulder. Adams pitched a perfect inning on Tuesday, striking out one and getting two groundouts.
"It was clean, it was good," Sandberg said of Adams' first rehab outing. "He has a couple days off, and he will do one inning again and then repeat that. I just heard that he did fine."
Adams hopes to pitch for the Phillies at some point in September. He's been on the disabled list since June 7.
Austin Laymance is a reporter for MLB.com. Follow him on Twitter at @jalaymance. This story was not subject to the approval of Major League Baseball or its clubs.