Franco will not play in at least games Thursday and Friday against the Kansas City Royals, Cash said.
"Wander is a really good kid, really good person," Cash said before Thursday night's game with the Royals. "He's a young player that is learning and dealing with the challenges of being a major league player, and some of the frustrations that come with it.
"Over the course of this season there's been probably multiple times that the way he has handled his frustrations have not been the way that we ask our players to uphold being the best teammate."
Cash declined to give specifics about any incidents, but the 22-year-old has not run out grounders at times and has had some baserunning lapses.
Also, Franco has thrown his bat after striking out, and last Sunday declined to talk to reporters after making two errors on one play.
"We're going to continue to support Wander as he works through this," Cash said. "I'm personally going to [help], this organization will, this staff will. We look forward to having him back."
Franco is hitting .287 with eight homers and 34 RBIs and has stolen 24 bases.