CINCINNATI -- Cubs first baseman Anthony Rizzo did not start Wednesday because of lower back tightness, which had forced him out of Tuesday's game.
Manager Rick Renteria said Rizzo would receive treatment Wednesday, and he could be back in the lineup Thursday.
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.