Bundesliga leaders RB Leipzig said on Tuesday Mali midfielder Amadou Haidara had tested positive for coronavirus after a previous test returned an ambiguous result, hours before their Champions League match with Istanbul Basaksehir.
Leipzig said the rest of their squad all tested negative for Covid-19 ahead of hosting the Turkish side in their opening game of the group stage which kicks off at 1900GMT.
The 22-year-old, who scored his first international goal in September's 3-0 friendly win over Ghana, has been isolated from the Leipzig squad since last Thursday as a preventive measure.
He was absent from Saturday's 2-0 win at Augsburg which kept Leipzig top of the German top-flight after four games.
"We are in continuous contact with Amadou Haidara, he is doing well given the circumstances and is not showing any symptoms," said Leipzig sports director Markus Kroesche.
"He is getting all the support he needs from us. We expect him back soon and wish him a quick recovery."
Haidara started Leipzig's opening three league games before being sidelined by the virus and scored in the 3-1 win over Mainz on the opening day of the season.