Bielak will start in place of Zack Greinke on Friday against Oakland after Greinke was placed on the 10-day injured list with neck soreness, Danielle Lerner of the Houston Chronicle reports.
Bielak's last major-league outing also came in a spot start Sept. 17 against Arizona. He logged 2.2 scoreless innings during that start before being optioned to Triple-A Sugar Land, although he returned to the Astros just two days later. Bielak figures to have a hard time working deep into Friday's game given that he hasn't eclipsed 3.1 innings all season.