Champions League: Bayern Munich's Serge Gnabry tests positive for coronavirus ahead of Atletico Madrid match
Serge Gnabry is the second member of the Germany squad to test positive for the virus after Manchester City midfielder Ilkay Gundogan.
The 25-year-old is "doing well" and is in quarantine at home, the German giants said in a brief statement.
He will miss Wednesday's Champions League group game against Atletico Madrid when Bayern begin the defence of their European title behind closed doors at the Allianz Arena.
However, Bayern did not say whether Gnabry's positive test would have any other impact the home game after he took part in the club's training session on Tuesday morning.
The former Arsenal winger has started all four of Bayern's Bundesliga games this season and scored a hat-trick in their 8-0 demolition of Schalke in the opening game last month.
He is the second member of the Germany squad to test positive for the virus after Manchester City midfielder Ilkay Gundogan.
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European champions Bayern Munich and Qatari side Al-Duhail, who qualify through being hosts, are the only teams yet confirmed for the competition with other continental tournaments around the world delayed by the coronavirus.
Cologne held on in Dortmund to end its 18-game run without a win in the league. Erling Haaland and Mats Hummels missed late chances for Dortmund.
Costa will miss Atletico's Champions League game at home to Lokomotiv Moscow on Wednesday and is expected to be out for at least a month.