Onuoha is likely to be forced out of Eastlands, as City boss Roberto Mancini goes on a summer spending spree and Everton boss David Moyes is keen to bring the 23-year-old to Goodison Park.
The former England Under-21 international can play anywhere along the back four, but has struggled to hold down a regular place for the Citizens with so much competition for places.
It's expected the Nigerian born defender, who arrived at City in 2004, will be allowed to leave in the summer having fallen down the pecking order.
Onuoha has made just seven appearances this term, scoring past Scunthorpe United last month in the FA Cup.
Moyes is keen to do a deal and hopes a fee in the region of £4m will be enough to secure the talented youngster's signature.