Hammel (4-1, 2.45 ERA), who was scheduled for Wednesday, now will go Thursday in the series finale at Busch Stadium against Michael Wacha (2-3, 2.85 ERA). Chicago's Jeff Samardzija (0-3, 1.45 ERA) will get an extra day of rest and start Friday at Wrigley Field against the Brewers.
The Cubs have another makeup doubleheader scheduled for July 8 against the Reds in Cincinnati.
Chicago manager Rick Renteria had rookie Mike Olt in the lineup Wednesday and most likely will stick with him for the finale of the rain-shortened series. Renteria has been trying to find the right matchups for Olt, who leads all National League rookies with eight home runs and 19 RBIs.
General manager Jed Hoyer knows there's some angst from Cubs fans when Olt isn't in the lineup.
"I think Ricky has done a nice job with Mike," Hoyer said Wednesday. "I get it -- I think people are excited to see him and people love homers. It's fun when he's in the lineup.
"I want him to play, too, but I also think matching him up and finding the right matchups, you want to make sure there are days when [Luis] Valbuena is in the lineup. There are days you really want [Darwin] Barney in the lineup because he's our best defender. There are a lot of factors at play.
"Frankly, I think it's helped Mike in the long haul adjusting to the big leagues and getting comfortable here."
The Cubs' third-base platoon of Olt and Valbuena entered Wednesday leading the National League with eight home runs and was tied for sixth with 24 RBIs. Hoyer said Valbuena is "underappreciated."
"He's got a low batting average but a really high on-base percentage," Hoyer said of Valbuena, who has a .226/.351/.387 slash line. "Last year, I think we were among the top 10 in baseball in production at third base with Valbuena and Donnie Murphy and [Cody] Ransom and those guys. The biggest part of the platoon was Valbuena."
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.