Duke was scheduled to start Thursday in the final game of a series at Cincinnati. Instead, left-hander Phil Dumatrait will start on four days' rest.
The Pirates plan to start him Friday against St. Louis.
Dumatrait, who was claimed off waivers from Cincinnati last October, is 1-2 with a 4.05 ERA in five starts and 10 relief appearances. He went 5 2/3 innings in a 5-4 win over the Cubs on Saturday night.