The move for the 31-year-old Nigerian striker is subjected to him passing a medical after the footballer was given permission to talk with the Saudi Arabian club, according to Mail Online Football.
It comes just days after his loan spell at Old Trafford came to an end, with the striker penning a heartfelt farewell to the fans.
The boyhood United fan said in a tweet: ‘It’s so hard to see this dream come to an end.
‘But I give God the glory for helping me fulfill this lifelong dream of putting on a Manchester United shirt as a player and represent this great club, it was indeed an honour I will forever cherish and be grateful for.
‘To the manager, I say thank you for trusting and believing in me when many did not. To my amazing team-mate, I will miss you guys, it was always fun… and I pray we win the league and FA Cup this year.
‘To the best fans in the world (the Manchester United fans) we have missed you, but we hear your voices cheering us on from afar, we can’t wait to have you all back in the stands. ‘I’m still and will remain a Manchester United fan forever. Once a Red, always a Red. Thank you Manchester United and God bless.’
Ighalo scored five goals across 23 appearances in all competitions for United.