The Cubs are opting to forego Donn Roach's spot in the rotation and will trot out newly-acquired Clayton Richard against the Marlins Saturday instead.
Richard was sent from the Pittsburgh Pirates to the Cubs Friday for cash considerations.
The 31-year-old lefty is 4-2 with a 2.09 ERA and 1.179 WHIP in nine starts for Pittsburgh's Triple-A affiliate in Indianapolis.
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Richard - who was ranked as the No. 3 prospect in the White Sox system before the 2008 season - was involved in one of the more high-profile trades in recent Chicago baseball history when he was sent to the San Diego Padres as part of the deal that brought Jake Peavy to the South Side.
Richard is 46-47 with a 4.33 ERA and 1.398 WHIP over parts of six big-league seasons. He was 6-8 with a 5.14 ERA in 39 games (22 starts) for the White Sox.
The Cubs have been searching for a consistent No. 5 starter for most of the season after Travis Wood was moved to the bullpen following a bout of inefficiency in the rotation.
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Tsuyoshi Wada was next up in the rotation but the veteran Japanese lefty landed on the DL last week with a shoulder issue, prompting the Cubs to call up Roach for one start in St. Louis last weekend.