Gray lasted just 1⅔ innings in his last start, allowing seven runs, all earned, on eight hits and a walk, failing to strike out a single batter.
Gray will face a strong Pirates lineup anchored by 2013 NL MVP Andrew McCutchen, who bats third and plays center field tonight. Hitting behind McCutchen is third baseman Jung-Ho Kang, who is hitting .323/.392/.579 with eight home runs since the All-Star break.
Not in the Pittsburgh lineup is former Rockies fan favorite Clint Barmes, with Jordy Mercer playing shortstop and batting eighth for Clint Hurdle's Pirates tonight.
On the mound for Pittsburgh is veteran southpaw Francisco Liriano, who has a 3.23 ERA and 1.17 WHIP in 147⅔ innings this season, though he has struggled in August, with a 5.06 ERA in four starts this month.
Rockies manager Walt Weiss has overloaded the lineup with right-handed bats against Liriano, with Charlie Blackmon and Ben Paulsen on the bench and Brandon Barnes and Matt McBride starting in their stead.
First pitch tonight is at 5:10 p.m. Mountain time and the game will be shown on MLB Network nationally in addition to the local broadcast on ROOT Sports.