The Serie A leader makes the trip to the Wanda Metropolitano on Wednesday for what shapes as a blockbuster tie, FourFourTwo reported.
Allegri is desperate for Juve to find a breakthrough in the Spanish capital, but he is wary of Atletico, which has reached at least the Champions League quarterfinals in four of the past five seasons.
"The team is in good shape. It is a two-legged challenge against a very physical team," he said after Friday's 3-0 win over Frosinone.
"Atletico plays very aggressive football when playing at home. It is a team that has had great results in previous years in Europe.
"It is an open match, we have as much chance to go through as they do.
"The first thing we must do is score a goal in Madrid. Scoring in Madrid will be decisive for our qualification."