The Chinese Super League side have agreed on a deal with United, which allows the 30-year-old to stay at Old Trafford until January 2021.
The initial six-month loan deal had expired May 31.
Shenhua says they decided to allow Ighalo remain with the Premier League club, due to the delayed start to the season and visa issues caused by the COVID-19 outbreak.
A club statement read: “In view of the uncertainty over the opening of the new Chinese Super League season and the uncertainty over foreign aid policy, Shanghai Greenland Shenhua and Manchester United have extended the loan for the Nigerian player, Odion Ighalo.”
United will pay a £6m loan fee and one-third of Ighalo’s £300,000-a-week contract.