Gallen will be promoted from Triple-A New Orleans to start Thursday's game against the Cardinals, Craig Mish of FNTSY reports.
Gallen is set to make his big-league debut after dominating in 14 starts for New Orleans, compiling a 1.77 ERA, 0.71 WHIP and 112:17 K:BB in 91.1 innings. The young right-hander will replace Pablo Lopez -- who is reportedly headed to the injured list with a shoulder injury -- in the rotation, and he should have a good chance to stick around if he holds his own.