Ighalo was due to return to China yesterday, but will now remain at Old Trafford until January 31 2021.
The boyhood United fan arrived in January and impressed before football came to a halt, scoring four goals in eight appearances.
United boss Ole Gunnar Solskjaer said: “They [Shanghai Shenhua] have been great towards us, allowing him to play for his dream club.
“It’s been a dream for him and hopefully he can finish what he started and win a trophy with us.”
The Reds do not have an option to buy Ighalo at the end of his loan term.
— Manchester United (@ManUtd) June 1, 2020