Redshirt freshman Trevone Boykin is the likely starter at quarterback Saturday. Boykin has played in three games this season, completing nine of 10 passes for 74 yards and a touchdown. He has 12 rushes for 122 yards.
Before Pachall's arrest, there was anticipation that Boykin could see action at tailback against Iowa State since Matthew Tucker is dealing with an ankle injury. The Frogs had already lost leading rusher Waymon James to a season-ending left knee injury sustained at Kansas three weeks ago.
"This is not about this season," Patterson said. "This about a young man's life, about a whole bunch of kids."
Pachall wasn't suspended after his failed drug test was revealed publicly. Patterson said at the time the quarterback had completed drug and alcohol counseling mandated by the university.
His former roommate, linebacker Tanner Brock, was among four TCU players arrested in February after a six-month drug sting. All four players pleaded guilty to guilty to marijuana delivery charges and were sentenced to probation.
AP Sports Writer Stephen Hawkins contributed to this report.