The Bavarian giants overpowered the Gunners at the Emirates Stadium three weeks ago and are overwhelming favourites when the two sides meet in tomorrow's second leg.
Lahm said that Bayern are aware that Arsene Wenger's men will be hungry for revenge but believes there is a gulf in class between the two sides.
"The difference between the clubs was enormous," The Mirror quotes Lahm as saying.
"Arsenal were not brilliant because they never had chances. Bayern was the owner of the game and the first goal changed the situation.
"Now Arsenal will have to show a strong reaction and, even though we are very confident, we know they will try to show some pride and play well. But if we don't obtain qualification it will be a disaster. That would be the biggest failure of the season."
Bayern have reached the final in two out of the last three years.