Cologne have announced three people at the club have tested positive for coronavirus - yet training will continue ahead of the Bundesliga's return.
The German top flight looks set to become the first major league to return to action as the world continues to deal with the Covid-19 pandemic.
Clubs are back in training with a mid-May resumption on the cards, but Cologne's arrangements have received a setback.
The club, 10th in the Bundesliga, said that "after three positive tests, three people at FC Koln are now in quarantine" - but also that "the group training can continue".
In a statement, Cologne said: "FC Koln had the entire team and coaching staff, along with the backroom staff, tested on Thursday for COVID-19. Three people tested positive, all are symptom free.
"The three people who tested positive will go into a 14-day quarantine at home. FC Koln will not confirm any names out of respect for the privacy of those affected.
"FC Koln's training can continue as planned, according to the hygiene and infection control measures that have been in place since April 6 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."
Olympique Lyonnais will seek millions of euros in damages as they face being deprived of European competition for the first time in a quarter of a century following the decision to end the Ligue 1 season, club president Jean-Michel Aulas said.
The French League (LFP) said this week it was ending the 2019-20 campaign amid the COVID-19 crisis, resulting in Lyon finishing seventh, outside of the positions that would offer a place in European competition for next season.
With some teams having played 27 matches and others 28, the LFP drew up the final standings according to a performance index - number of points per game weighed by head-to-head record.
Aulas argued the season could have been finished in the form of playoffs behind closed doors in August and that the ranking method was disputable. "We see that these standings are illogical," he explained.