The former Norway boss (pictured) insists the Scottish champions are favourites to reach the group stages but does not think his side have to take a lead to Glasgow for the return game to have a chance of upsetting the odds.
Hareide pointed to the third qualifier against Slask Wroclaw, where Helsingborg went through 6-1 on aggregate after an impressive 3-0 first-leg win in Poland, when claiming a clean sheet against Neil Lennon's side was imperative.
"The most important thing is not to let Celtic score an away goal," he told Press Association Sport. "That is the key to the tie. If they do score it will be very difficult for us.
"We don't necessarily need to take a lead to Parkhead. We had a good experience in Poland in the second qualifier, we did really well there and we defend well when we stick together.
"Celtic are favourites, they are a big club with good players. But expectations are high in Helsingborg with regards to Europe and the fans will be behind us at home.
"We have a good record there, I think we have only lost one game in two years, so we are strong and we played very well in our last home game (a 7-2 win over Kalmar).
"It will be an interesting tie. Tactics are important over two legs and things can change from one game to the other but we have to go into the game in a positive manner."