The Red Devils will also receive just under half of the £ 300,000 Nigerian salary.
Ighalo was set to return to the Chinese side after spending four months on loan at Old Trafford, but with the Premier League season ready to boom, United wanted to keep the attacker.
They have successfully negotiated, but will end up paying Shanghai Shenhua £ 10.5 million by the end of the deal.
United paid Ighalo £ 130,000 a week and a £ 6m loan fee.
The English club has no option to buy the striker after the extended deal ends on January 31.
This means Ole Gunnar Solsjkaer can also call on the Nigerian for a period next season.
United’s attempt to keep Ighalo has been helped by the fact that the Chinese Super League has no fixed date for its next season.
China also told foreign nationals late last week that there would be no visa to return to the country until October.
No emergency visa would have been granted to those involved in the Chinese Super League, which means that Ighalo could not have played for the club had he returned from Old Trafford.
A statement from the club said, “Given the uncertainty surrounding the opening of the new season of the Chinese Super League and the uncertainty regarding foreign aid policy, Shanghai Greenland Shenhua and Manchester United have made a loan to Nigerian player Odion Ighalo. “
Ighalo has scored four times in eight games with the Red Devils.