Rizzo, who hit his 30th home run on Tuesday in the Cubs' 3-0 win over the Reds, has started 129 of the team's 132 games.
He is the first Cubs left-handed hitter to reach 30 home runs in a season since Fred McGriff belted 30 in 2002. A Cubs left-handed hitter has totaled 30 home runs in a season 11 times, including five by Hall of Famer Billy Williams. Williams owns the franchise record for most home runs by a lefty, hitting 42 in 1970.
Chris Valaika started at first base Wednesday for the Cubs.
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.