"I'm going to shut it down for today and tomorrow, too," Rizzo said Saturday. "I hit, I ran. Hitting felt all right. I took two rounds, let it calm down, hit again. Then I ran for the ultimate [test]. Jogging [is a problem].
"It felt a lot better today than yesterday, so I think if we let it rest, it'll be OK," he said. "I don't want to come back and then miss the rest of the season if I'm really bad. I can wait a couple days to play the rest of the season."
So far, the diagnosis is nothing more than lower back tightness.
"I just locked up," he said.
Rizzo has had minor back problems before, but never for this long. Could he return for the Cubs' home game Monday against the Brewers?
"It's day to day," Rizzo said. "I'll be out today and tomorrow. If I wake up [Sunday], we'll re-evaluate. But as far as baseball stuff, we'll be done until Monday."
Rizzo has yet to be in the same lineup as top prospect Jorge Soler, who hit two home runs Friday in the Cubs' 7-2 win.
"This is an important month," Rizzo said. "The better we do now, the better we go into the offseason, the better we go into Spring Training, and everyone else feels it."
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.