Pachall injured the left arm during the No. 24 Horned Frogs' 38-17 win Saturday against Southeastern Louisiana. He had surgery later Saturday to repair the forearm fracture, which could keep him out until early November.
As a result, Trevone Boykin will take over for Pachall at quarterback for the second consecutive season. Boykin started nine games in 2012 after Pachall left the team to seek treatment for substance abuse addiction.
In the opener against LSU last week, Boykin replaced Pachall and played most of the second half. TCU coach Gary Patterson started Pachall again against Southeastern Louisiana while playing Boykin at receiver. Boykin caught three passes from Pachall for 25 yards, before sliding back to quarterback after Pachall's injury late in the first half.
TCU travels to face Texas Tech this Thursday night.