Real Madrid and Barcelona are fancied to win the Champions League but the Spanish giants need to be wary of the threat posed by English sides, according to Brazil legend Ronaldo.
The LaLiga teams have dominated the competition in recent seasons with Madrid winning four and Barca one of the last five.
Liverpool came close to breaking their stranglehold on the competition last season but stumbled at the final hurdle as a Gareth Bale-inspired Los Blancos wrapped up a third consecutive title with a 3-1 win in Kiev.
While Ronaldo – who played for Barca in the 1996-97 season and for Madrid between 2002 and 2007 – expects one of his former clubs to lift the trophy again, he concedes that an English side are more than capable of claiming a first title since Chelsea did so in 2012.
"The favourites to win the Champions League are the same: Real Madrid and Barcelona," he told Omnisport.
"Real Madrid because of their history and tradition. They won four of the last five, and the last three in a row. So Real have an important place in this competition.
"Many teams have been reinforced a lot. This competition is very difficult, you need to know how to play it well.
"When the group stage finishes you have the knockout stage. It's a very fun and beautiful competition, but you need to know how to play it in order to go all the way.
"The Spanish teams know this very much, but I believe we could have surprises from the English teams.
"They are very strong and they have financial support to buy and sell players - I believe in them."