Juve – eight points clear of Roma at the top of Serie A – are away to in-form Samp on Sunday and their head coach thinks that fixture may present a tougher test than next month's Barca tie because his players could get caught out by a lack of urgency.
Allegri insists the league remains the top priority as the Bianconeri seek an unprecedented sixth consecutive title and does not want his players to get distracted after being drawn against Luis Enrique's side.
"It will be a fascinating match [against Barca], but Sunday is the most difficult of them all because you don't need to find motivation against Barcelona," he said.
"Samp have beaten Roma, Milan and won the derby with Genoa. They have won five and drawn two of their last seven matches, so we need to be on top of our game.
"Barcelona will be a big clash, but there is no point talking about it now. I want a game of that magnitude to feel very normal, not a special event – we have been in this position regularly recently and last year we were unlucky to draw Bayern Munich.
"There are 10 games left in Serie A, Roma and Napoli have the potential to pick up 30 points, so we don't have first or even second place under lock and key.
"If we don't play Samp with a serious, responsible attitude, we could find Roma five points away."
Allegri added: "Our primary objective is to win the Serie A title because six consecutive Scudetti is something historic that has never been done, it would be extraordinary.
"We need to be careful of ourselves. Sampdoria have enthusiasm, Marco Giampaolo has given a real tactical identity to the team and they have nothing to lose.
"After winning the derby, they will try to make a dream come true by beating Juventus. If we don't have the same motivation as then, we are in real trouble."