Juventus coach Massimiliano Allegri hailed Cristiano Ronaldo, saying it was "impossible to think" the star had just one Champions League goal this season before Tuesday's heroics.

Ronaldo produced a special display, scoring a hat-trick to guide Juve to a 3-0 win over Atletico Madrid, sending them through to the quarter-finals 3-2 on aggregate.

The Portuguese star had scored just once in his six games prior in the competition this season, a run that surprised even Allegri.

"It's impossible to think Cristiano with only one goal scored in this Champions League," he told a news conference.

"He scored because he played well in the box and his team-mates worked well in the gameplay.

"A great match with an outstanding crowd supporting us and the players gave all Italian football fans a real show. That's the most important thing."

Ronaldo's arrival had seemingly made Juve one of the favourites in the Champions League, which the Serie A champions last won in 1996.

But Allegri played down expectations, saying his side were just one of several contenders.

"Juventus is not the favourite to win the Champions League. We are one of the contenders and the trophy is one of our goals for this season, as usual," he said.

"If we were eliminated it would have not been a failure. Juventus every year must play the Champions League and today, I repeat, we get to the next stage. Because if you don't pass the round you don't have any chance to win. It is very simple.

"You don't need to graduate at Harvard to understand it – if you pass the group stage [you] have more chances, if not you play Europa League or watch the others from your sofa."