Gladbach said 20-year-old defender Jordan Beyer tested positive in a sample given Thursday.
The club said it consulted with local authorities, who did not require other players or staff members to isolate because of contact with Beyer. Their game Saturday against Union Berlin "is not affected in any way," Gladbach said.
Schalke didn't identify its infected player but said he was in home isolation after results came back from tests administered Thursday. All other players and staff who were tested had negative results, and the player had previously tested negative Tuesday, the club added.
The news adds to a litany of coronavirus-related woes at Schalke. The club has been hit harder than most by the loss of game-day revenue during the pandemic and is trying to impose deep spending cuts. There was also a positive coronavirus test for an unidentified player during a pre-season training camp in Austria.
Schalke plays Bremen on Saturday in a game between two former title challengers who have fallen on hard times.
Schalke has not won a league game since January and was beaten 8-0 by Bayern Munich last week. Bremen only narrowly avoided relegation in a playoff at the end of last season and is coming off a 4-1 loss to Hertha Berlin.
