The Portuguese outfit take on the Hoops at Parkhead in their group stage opener on Wednesday night and Aimar is tipping Neil Lennon's men to put in a much better shift than their last two league matches in which they have recorded just one point.
"Celtic have failed to win in the league for the past two weeks but I don't expect that to have an influence on what happens on Wednesday," said Aimar.
"Celtic always change their level, especially at home in the Champions League, and I expect them to be far more dangerous when they play us."
But in saying that, the former Argentina international is confident of getting the required result to kick-off their Champions League campaign.
"We're convinced we can win in Scotland. We're technically a better side than Celtic and we're going there for a victory," he added.
"The key for us is to score the first goal. If we can get ahead early they will suffer some nerves which would allow us to create more chances.
"I'm expecting an intense match but we have shown we can play to a good level in Europe."