The French midfielder had to be substituted in the 37th minute of the Gunners' 4-1 home win against Norwich City in the Premier League on Saturday.
"He had concussion," Wenger told reporters. "He had double vision, so on the advice of the doctor I took him off because I did not want to take any gamble.
"I don't know if he'll be available for Dortmund, it depends now what the doctors will decide.
"Sometimes they are not allowed to play for five days, it depends how big the concussion was.
Arsenal will host Dortmund at the Emirates Stadium on Tuesday.