Gonzalez went 0-for-4 in Monday's loss with a strikeout and found out after that game that he'd be out Tuesday.
Mattingly said that Gonzalez wasn't hurt, just getting a break.
"He's good," Mattingly said. "I could see him getting tired. When I talked to him about it, I could tell he wasn't fighting me."
Gonzalez is 5-for-28 on the road trip and is tied for second in the National League with nine homers and tied for third with 25 RBIs.
Jeff Seidel is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.