The 24-year-old attacker expects goalscoring opportunities to be at a premium at Signal Iduna Park, though the German side have been boosted by the return of Sebastian Kehl
And the Germany international has urged his team-mates to take whatever openings that they can create at Signal Iduna Park.
"It will be extremely difficult and I don't expect we'll get as many opportunities as we did against Stuttgart," Reus told Ruhr Nachrichten.
Napoli, Arsenal and Dortmund are all on six points after the first three matches in Group F and a win on Wednesday would put breathing space between BVB and Arsenal.
The Germans, who currently sit second in the Bundesliga, have also been given a boost ahead of the match after it was revealed that defender Sebastian Kehl has recovered from injury.
"I am ready to be in the squad again," the 33-year-old announced.