Rizzo was batting .211 (8-for-38) in his last 11 games, with one double as his only extra-base hit and three RBIs.
"He's not feeling right at the plate and it's snowballing a little bit now, so you want to stop that from snowballing any further and let him kick back and work with [Rowson] today and get things ironed out," Cubs manager Dale Sveum said.
Part of the problem, Sveum said, is Rizzo may be "thinking too much and trying to do too much all the time instead of just letting it happen."
Rizzo was the National League Rookie of the Month in July, batting .330 with seven home runs and 17 RBIs in 25 games. He's hit one home run in August.
"Who knows the reason why," Sveum said of the dropoff in power numbers. "To me, it's more a young man who got here and was obviously on top of the world and doing everything, and unfortunately, sometimes in this game, if you try to tell some young guys that for some reason, when you're going good, you're putting yourself in line for a slump sometimes. Why that happens is a million-dollar question in hitting -- why all of a sudden you're on top of the world and the next day you feel like you're on ice skates in the batter's box. That's why you give guys day off and give them a chance to regroup."
Rizzo was batting .283 overall with nine home runs in 55 games since he was promoted in late June.