The Greek club are currently top of Group C on four points, and Townsend believes that their promising start in the competition proves that Spurs are in for a tough challenge at White Hart Lane.
"We know we've got the quality to win our matches," the England winger told the club's official website. "This is a game we need to win in front of our home crowd and we need to get three points.
"We've played against Partizan and Besiktas already in the group, and for Asteras Tripolis to have done well against those sides and be top of the group after two games shows how much we need to take them seriously."
Spurs have drawn with Partizan and Besiktas in their opening two fixtures.