Madrid sit level on points with their capital rivals, while Barcelona are one point behind the top two in third spot.
"I watched El Clasico one day afterwards because I was flying while they were playing. It was a great match and a great advert for Spanish football throughout the world," Capello told EFE.
"Of course we will see a different league now, but we also need to see how it affects the Champions League. I think Madrid have the most possibilities, because they have the biggest squad and are playing very well. Barca have gone back to being the team the whole world knows. Atletico have surprised me but I saw them play against Barca in Madrid."
"Atleti have a huge desire and strength, but they have a thin squad. When they play in the Champions League against Barca we need to see what will happen in the following league games. They are playing very, very well. They are very compact and have a winning mentality."
All three title rivals are in action on Wednesday evening.