Former Real Madrid and Barcelona striker Alfonso has described Sunday's Clasico as Lionel Messi versus Cristiano Ronaldo.
LaLiga leaders Madrid head into the match at Santiago Bernabeu with a three-point advantage over the champions, with a game in hand too.
Zinedine Zidane's side warmed up for the game with a 4-2 Champions League quarter-final second-leg victory over Bayern Munich, in which Ronaldo hit a hat-trick to become the first player to score 100 goals in the competition.
Messi has been in formidable form himself despite Barca's inconsistent results, with the Argentina star on 45 goals and 17 assists from just 44 appearances in all competitions.
Alfonso, who won LaLiga with Madrid in the 1994-95 season and spent two years at Camp Nou later in his career, believes the entertainment factor of watching Spain's top two go head-to-head is made greater by seeing Messi compete with Ronaldo for personal supremacy.
He told Omnisport: "Nowadays, El Clasico can be seen anywhere around the world. In my time it wasn't like that. Football has developed in every way.
"On top of that, you have players like Lionel Messi and Cristiano Ronaldo. Everyone wants to see them playing against each other. It's not just Real Madrid versus Barcelona - but Messi versus Cristiano.
"A game between Real Madrid and Barcelona has a huge impact. They both compete for the La Liga title. If you lose one of the games it hurts and if you win it's a great joy. At the end of the game some players are left celebrating and others are sad.
"It's especially important in the eyes of the fans. In football terms, there are just three points at stake – [ones] that you could earn at any other point in the season if you miss out."
