The Nigeria international, a lifelong United fan, joined the club on loan from Shanghai Shenhua in January due to the Covid-19 situation then prevailing in China.
But the virus then spread to Europe and brought the Premier League season to a halt in mid-March.
It looked then as if the 30-year-old's career with United might amount to just eight games given his original deal was due to expire on 31 May.
But ahead of the Premier League season resuming on 17 June, United said Monday they had agreed with Shenhua to extend Ighalo's loan move until January.
"I'm really happy. It's a dream for me to be here. I'm buzzing and ready to go," Ighalo told MUTV.
"The last few days have been difficult as there have been different talks about it but now I'm really happy, so I need to concentrate fully".