Ünal signed for Genk on a two-year loan deal over the summer transfer window but his contract has been terminated by mutual consent.
Genk have also released a statement confirming the transfer on the official club website.
The 19-year-old striker struggled for playing time at the Belgium side after a bright start to his stint at Genk.
Ünal did manage to score twice in 12 appearances for Genk but scored played just two minutes over the last seven games.
The Turkish international striker was signed by City on a £2 million transfer from Bursaspor but was unable to play in England due to failing to get his work permit.
City loaned Ünal out to gain playing time and experience in Belgium but despite signing a two-year deal with Genk the Premier League giants had the option to bring the youngster back at the end of the first season.
Ünal made a name for himself scoring 182 goals in 110 appearances for Bursaspor’s reserves and 24 goals in 25 international games for Turkey at under-16 level before being fast-tracked into the under-19, under-21 sides and senior national sides.
The 19-year-old also holds the record for being the youngest goal scorer in the Turkish Super League when he scored against Galatasaray in 2013.