United States international John Brooks was taken off with a thigh problem just 37 minutes into his competitive debut for Wolfsburg.
Wolfsburg, the 2015 DFB Pokal winners, secured their passage to the second round of the competition on Sunday with a 1-0 win at Eintracht Norderstedt thanks to Ignacio Camacho's second-half strike.
At that point, Wolfsburg were already without Brooks, who was forced to leave the pitch with an injury eight minutes from the half-time whistle.
"We will see how bad it is after further examinations," Wolfsburg coach Andries Jonker told reporters after the match.
Kicker reported on Monday that Brooks faces a challenge to return in time for Wolfsburg's Bundesliga opener against Borussia Dortmund on Saturday.
The defender became the most expensive U.S. player ever this summer when he left hometown club Hertha Berlin for Wolfsburg for a reported fee of €20 million.
Brooks will hope to be part of the U.S. side that faces Costa Rica in a World Cup qualifier on Sept. 1.