Three people at Cologne have tested positive for coronavirus, the German club have confirmed, although they say training will "continue as planned".
The Bundesliga is set to become the first major football league in Europe to return to competition.
Officials suggested a resumption on 9 May but government delayed the decision and a restart may now be 16 or 23 May.
Those who tested positive are "symptom free" but will remain in quarantine for 14 days, said the club.
"The entire team and coaching staff, along with the backroom staff, tested on Thursday for Covid-19," the statement added.
"FC Koln will not confirm any names out of respect for the privacy of those affected. Training can continue as planned, according to the hygiene and infection control measures that have been in place since 6 April in group training.
"The prerequisite for this is that the relevant group of people are tested further, as stated for in the medical concept of the 'Taskforce Sports Medicine/Special Game Operation' from the DFL."
On Thursday, Chancellor Angela Merkel said that any decision on if and when sports activities could resume would now be taken on Wednesday, 6 May.
The league has been suspended since mid-March because of the global coronavirus pandemic.
"It is absolutely necessary that we remain disciplined and stick to health guidelines," said Merkel.
The DFL has warned that many top-division teams will be in an "existence-threatening" financial position if play does not resume by June.
With nine games of the season remaining, Cologne sit in 10th place.