Real Madrid goalkeeper Iker Casillas has claimed Atletico Madrid and Bayern Munich are Los Blancos' main rivals in their attempt to defend the Champions League title this season, ruling out other big clubs such as Chelsea and Barcelona as their main competition.
After beating both the German giants in the semi-final and Diego Simeone's side in the final last season, Los Blancos secured their 10th European Cup/Champions League title. Now they are hoping to become the first club since the competition was rebranded in 1992 to win the title in successive seasons.
Real manager Carlo Ancelotti's side have enjoyed an impressive start to the campaign in both La Liga and the Champions League.
Having won the last 18 games in a row, the Spanish giants are leading La Liga two points ahead of Barcelona and have also guaranteed a spot at the top of Champions League Group B after winning all five games.
Meanwhile, Chelsea have experienced a similar start to the season both in the Premier League and the Champions League.
Jose Mourinho's side are leading the domestic competition, three points ahead of Manchester City, while with one game to go against Sporting Lisbon they have also secured Champions League qualification as leaders of Group G.
However, when questioned about Real Madrid's biggest rivals when it came to winning the Champions League, club captain Casillas said: "In Europe? Bayern and Atletico Madrid."
Meanwhile, the goalkeeper said Simeone's side and Barcelona will be their main concerns in La Liga and the Copa del Rey.
"Atletico Madrid and Barcelona are our rivals in domestic competitions, and I think they'll both fight until the end for the League," he said, according to AS.
"We also hope [to fight for La Liga] because we're doing really well at the moment.
"We've done well this year and what better way to put the icing on the cake [than win the Club World Cup]?"