Davis, 35, will be making his first start in the Major Leagues since July 9, 2010, when he faced the Pirates. He was 1-4 with a 7.51 ERA in eight starts last year with Milwaukee, limited because of a heart problem and flexor tendon surgery on his left elbow.
The lefty signed a Minor League deal with the Cubs on April 12 and reported to extended spring training in Mesa, Ariz. Cubs general manager Jim Hendry and pitching coach Mark Riggins watched Davis throw on April 30 in Arizona, and the pitcher then made one start for Class A Daytona May 5, in which he threw 6 2/3 scoreless innings, giving up two hits.
He started Tuesday for Triple-A Iowa in Colorado Springs and gave up two runs, four hits and struck out five over 3 2/3 innings. He threw 59 pitches, and the outing was cut short because the Cubs decided he was ready and needed him Saturday.
"He's a Major League pitcher," Hendry said Wednesday. "He used to give us fits. He's a different kind of guy -- he's got that pause in his delivery."
Davis has pitched for the Rangers, Diamondbacks, Blue Jays and Brewers, and in 12 seasons compiled a 91-101 record and 4.38 ERA.
"He looks like he's back where he used to be," Hendry said. "I thought he had maybe a little more crispness when I saw him in Mesa [in April] than he did his last year in the big leagues."
The Cubs have used lefty James Russell as the fifth-starter fill-in for Andrew Cashner, who went on the disabled list April 6 with a strained right rotator cuff. Russell was 0-4 in four starts and now is back in the bullpen.