Toulon's English fly-half Jonny Wilkinson says he is wary of Premiership leaders Harlequins which the French club will meet Friday in the Challenge Cup quarter-finals.
Despite winning the World Cup title with England in 2003, Wilkinson has never lifted a European trophy.
He came closest two years ago when Toulon lost the Challenge Cup final to Cardiff Blues (21-28) in a match during which he hobbled off injured.
"We're expecting to play a match on a par with the Heineken (European) Cup.
"Harlequins have just had a great match against Saracens (24-19 win last Saturday in Wembley).
"In the final 10 minutes and while they were down to 13 players they didn't give up. It was very impressive.
"They showed that they are capable of beating any team. They could very well take on the Top 14 leaders.
"They should be considered as equal to Toulouse or Clermont."
He added: "It's a team that can vary their style of play and score at any time. They have a unique spirit.
The players are very united, in defence, in attack and that's why they are leading the championship."
Wilkinson added that his team would have to be on the top of their game to get a win.
"Against a great team like that you know that if you're not at 100 percent and if you don't manage to keep up the necessary intensity and focus for the entire 80 minutes it's going to be tough."
Harlequins will be without England captain Chris Robshaw for this match.