The Belgian, who joined Chinese Super League side Shandong Luneng in January 2019, is currently under isolation at Jinan hospital, which specialises in treating infectious diseases.
Fellaini, who spent 11 years in England with United and Everton, had recently returned to China from Dubai after leaving the country following the Covid-19 outbreak.
“The official test confirmed that the player Fellaini has tested positive for the coronavirus during the quarantine observation period,” Shandong Luneng confirmed in a statement.
“During this period, the player’s body temperature has been normal and there are no other discomforts. He has received further observation and treatment at a designated medical institution.”
On Saturday evening, Juventus forward Paulo Dybala and AC Milan director Paolo Maldini both confirmed they have contracted coronavirus and are now under quarantine in Italy.
“Hi everyone, I just wanted just to inform you that we have received the results for the Covid-19 test and both Oriana and I have tested positive,” Dybala, who is the third Juventus player to test positive, wrote on Twitter.
“Luckily we are in perfect conditions. Thanks for your messages.”
In England, Portsmouth confirmed that four players – James Bolton, Andy Cannon, Sean Raggett and Haji Mnoga - are in self-isolation after testing positive for Covid-19, while the club waits on further results for the rest of its players and staff.
In a statement, the club’s chief executive Mark Catlin reassured that the players were “in good spirits and perfectly calm” and added: “Football is not immune from this virus and I can assure you that it only really hits home when those that you know contract it.
“We once again urge everyone to follow the current government guidelines.”