Sisk was placed on the 15-day injured list Saturday with left elbow inflammation, Colin Beazley of the Pittsburgh Post-Gazette reports.
The 29-year-old southpaw has a 2.23 ERA, 1.18 WHIP and 43 strikeouts in 36.1 innings out of the Pirates' bullpen this year. Hunter Stratton was recalled from Triple-A to take Sisk's place in the bullpen.