City have the option to cut the loan stay short at the end of the season.
The 18-year-old striker joined the Citizens on a £2 million transfer from Bursaspor last month and joined the senior side on tour in Australia.
Ünal made a number of appearances in the International Championship Cup including the victory over Roma on penalties.
The Turkish international has also confirmed the move via his Twitter account and also thanked City for taking him on the summer tour.
Ünal became the youngest player to score a Süper Lig goal when he netted against Galatasaray in 2013 aged just 16.
The 18-year-old already has one senior international cap and scored 24 goals in 25 games for Turkey’s under-16 side.
Genk play in the Belgium Pro League and the young striker is expected to gain first-team experience next season.