Kiongera, whose contract with Tanzanian giants Simba expired last month, had agreed a move to the den subject to terms and conditions.
Meanwhile Gor Mahia's Secretary General Ronald Ngala, says the club has planned ahead and will get a cover, in case midfielder Khalid Aucho, who is set for trials with Glasgow Rangers, leaves Kogalo.
The Ugandan international helped Gor clinch a double last season and has been the pillar in their midfield.