The left-hander will take Adrian Sampson's spot in the rotation.
Allard was acquired last week in a deal that sent reliever Chris Martin to the Atlanta Braves.
Allard was the 14th overall pick by the Braves in the 2015 Draft out of San Clemente High School in southern California. He throws a low-90s FB with a good cutter and strong change. He’s working on his curveball and, in general, improving his out pitch. He’s got great command and his current skillset profiles as a No. 4 or No. 5 starter.
In his first start with Triple-A Nashville on August 3, he threw five shutout innings, allowing four hits, two walks and struck out eight.