The loan signing from Shanghai Shenhua has been working at another facility in Manchester with a personal trainer.
The Times claims Ighalo has been ordered to stay away from the rest of his team as a precaution.
The Nigerian forward has not been diagnosed with the virus - but was told to quarantine himself from United's AON Training Complex for health and safety reasons.
United's squad is currently on a warm-weather training camp in Marbella, Spain, during the Premier League's winter break.
Ighalo did not join his teammates due to border restrictions placed on travellers who have been in Chinafor the past 14 days.
United were concerned UK immigration could tighten border restrictions after the World Health Organisation upgraded the coronavirus outbreak to a global emergency.
The club said that "it is simply a precautionary measure as the situation continues to be monitored".