Cubs manager Lou Piniella said the problem isn't serious. Lilly is rehabbing from arthroscopic surgery on his left shoulder, which he had in November. He was to make two more Minor League starts before given the go-ahead to join the Cubs' rotation in mid April.
"This is not a setback," Piniella said of Lilly's back soreness.
The lefty last pitched Sunday in Mesa, Ariz., in the Cubs' Minor League camp, throwing 67 pitches over 5 2/3 innings.
The Cubs also have tweaked their rotation and will have Carlos Zambrano start Saturday rather than lefty Tom Gorzelanny. This was pitching coach Larry Rothschild's original plan, Piniella said, because they wanted to have right-handers face the Milwaukee Brewers next week at Wrigley Field.
Carlos Silva will make his first start for the Cubs on Friday in Cincinnati, followed by Zambrano and then Gorzelanny. Ryan Dempster will get the call for the home opener Monday. He will be followed by Randy Wells and then Zambrano again.
"Then we'll go from there," Piniella said.