AC Milan coach Carlo Ancelotti believes Liverpool are the hardest team to play against in Europe.
The Reds overturned a 3-0 deficit to beat Milan on penalties in the UEFA Champions League final in 2005 and they have consistently excelled in the competition in recent years.
Liverpool crushed Real Madrid last month to advance to the quarter-finals, while they are also mounting a strong challenge for the Premier League title.
Manchester United remain in pole position to clinch top spot but Ancelotti admits he is always more wary of Liverpool.
The Italian has great respect for Rafa Benitez and feels the Merseysiders can be unstoppable at times.
"Liverpool are the hardest team to play against in Europe," Ancelotti said in the Daily Mirror.
"Benitez is a great coach. He has a well-organised defence and the perfect counter-attack.
"To play against them is always dangerous. Manchester United are stronger, but they let you play. Liverpool don't."
Ancelotti, who has been linked with the manager's role at Chelsea, has also paid tribute to Guus Hiddink.
Hiddink will stay in charge of the Blues until the end of the season and Ancelotti would not be surprised if he was successful at Stamford Bridge.
He explained: "Hiddink is the coach I regard most highly. Professionally he is really good.
"He has done well everywhere he has gone. I like him as a person."