Gundogan was subbed off just before half-time in his team's 3-0 friendly win over fourth-tier side Kickers Wuerzburg on Tuesday and Dortmund coach Juergen Klopp confirmed after the match the 22-year-old midfielder might miss the cup clash with Wilhelmshaven.
The match with fourth-tier Wilhelmshaven will be Dortmund's second competitive fixture of the season, following their 4-2 win over Bayern Munich in the Super Cup last week.
Klopp conceded after the win over Wuerzburg that he was disappointed Gundogan had gotten injured after warning his players to take it easy during the friendly.
"We shouldn't act like we are fighting for the World Cup every day," Klopp said.
"Today it was important to move around, try out stuff and not get any injuries.
"It didn't turn out totally as we planned because Ilkay Gundogan is slightly injured.
"What counts is the match on Saturday in the first round of the DFB Pokal."
Dortmund hit the front on Tuesday thanks to a smart finish on the half-hour mark from new signing Pierre-Emerick Aubameyang, while 19-year-old striker Marvin Ducksch struck a second-half brace, including a fine volley to make it 3-0.
While Klopp was pleased to see his team notch their fifth win of pre-season, he maintained Dortmund must improve before the Bundesliga begins on August 10.
"I always want to see 100 per cent from my team but we are still working and our performance tonight was fine for this stage of pre-season," Klopp said.
"We played a great match on Saturday (against Bayern) and an average one today and that's fine."
