AC Milan goalkeeper Gianluigi Donnarumma and winger Jens Petter Hauge tested positive for Covid-19 three days after playing against Celtic in the Europa League.
Donnarumma played the full 90 minutes at Celtic Park, while Hauge came off the bench to seal Milan's 3-1 victory in Glasgow.
Milan say three staff members have also tested positive for Covid-19, with all five individuals asymptomatic.
They have immediately entered isolation in their homes and the relevant local health authorities have been informed, the Italian club said.
The results followed swab tests carried out on Sunday evening and Milan say there have been no other positive results following further tests of players and staff carried out on Monday.
Celtic, who are due to travel to play Lille in the Europa League on Thursday, have already been without players due to coronavirus issues.
France Under-21 international Odsonne Edouard and Israel defenders Nir Bitton and Hatem Elhamed have all missed Celtic's last three matches following positive Covid-19 results while on international duty.