Ighalo insists he initially thought the links to Manchester United were a joke, stating there were numerous factors against him.
The 30-year-old signed a six-month loan deal back in January, however, and has since extended his deal until January 2021.
"I thought it was a joke," Ighalo told Sky Sports. "I was playing in Shanghai. That was against me. Would a club as a big as United be looking in China for a striker? That was against me.
"My age. That was against me. There was a pandemic in China. That was against me. I said no this is a joke. Later when it got serious, I thought only when I fly to Manchester will I believe it."
He added: "When I signed, a lot of people doubted my ability. I never doubted myself and I knew what I could add to the team and I think I can still do more.
"People have not seen my best because I came in and my sharpness and fitness wasn't there, but I'm getting much better and I hope to finish the season really well."