The Gunners, who sit top of Group F on six points, face last season's beaten finalists in back-to-back gameweeks in Europe's elite competition.
Despite being in pole position to qualify for the last-16 stage of the tournament, though, Wenger says that two defeats against the German giants would drastically alter the complexion of the group.
Speaking to UEFA.com, he said: "Dortmund have grown a lot and they look a different proposition now.
"I feel we are stronger as well this season, so I think it will be very interesting.
"It is already a very important tie because usually [matchday] three and four usually are decisive, so that could be the key for us to qualify."
The North London outfit hosts Jurgen Klopp's men at the Emirates Stadium on Tuesday, before travelling to Signal Iduna Park for the return fixture on November 6.