Ünal has also confirmed the move via his Twitter account and also thanks the club for letting him join the senior team on the summer tour.
The Turkish international join City on the pre-season Australia tour and made an appearance in the 5-4 win over Roma on penalties last Tuesday.
The 18-year-old striker will not be playing in England next season due to not having the necessary work visa requirements, he would have to be granted special permission by the FA to play football in the Premier League for the 2015-16 campaign.
Ünal holds the record of being the youngest player to ever score in top-tier football in 2013 when he scored against Galatasaray and made his international debut aged 17.
Genk play in the Belgium Pro League and Ünal is expected to gain first-team experience next season.