The deal is however awaiting confirmation from the FA for registration.
A new contract with his parent club Shanghai Shenhua, will be discussed after the loan with United ends.
Ighalo initially arrived at Old Trafford in January this year and that deal expired May 31.
However, the Red Devils have been keen to keep the 30-year-old, after he impressed during his short stint.
The Nigerian striker has scored four times in eight appearances for Ole Gunnar Solskjaer’s side.