Coach Paul Rhoads announced Gannon's return on Monday. Gannon says in a statement released by the school that he has been diagnosed with anxiety issues and is receiving treatment.
Gannon opened the season as Iowa State's starting right tackle. But he left the team just days before a loss to Kansas State.
Rhoads announced Gannon's return just hours after he said backup lineman Jacob Dunning would miss the rest of the season with a ruptured patella tendon.
The Cyclones (1-2) next host No. 7 Baylor on Sept. 27.