The former Barcelona attacker has stated that the current Ballon d’Or holder is ‘swallowed up by his own ego’.
The Catalan hosts go into the game as favourites due to imperious recent form, with Lionel Messi displaying arguably the best performances of his career since the turn of the year.
The Argentina international was crucial in eliminating Manchester City from the Champions League in midweek and has overtaken perennial rival Cristiano Ronaldo at the top of the La Liga goalscoring charts.
Carlo Ancelotti’s men have gone off the boil at the same time, with their key player not playing to his best.
With Messi and Ronaldo set to renew their personal battle in Sunday’s blockbuster clash, Stoichkov has stated that the Barcelona man is superior - and the Real Madrid star knows it.
“Barca is the better team as of the moment; they’re fresher,” the outspoken Bulgarian told AS.
“Everyone says (Messi is better than Ronaldo). It must be for a reason.
“The problem is when you don’t recognize it. And then you end up being swallowed up by your own ego.
“Messi has won the four previous Ballon d’Ors. We’ll see if he (Ronaldo) gets to four. But judging by the way his team is playing, he’ll never do it.”
Ahead of the clash, Barcelona are one point ahead of Madrid, with 11 games remaining in the season.
The Clasico rivals avoided each other in the Champions League quarter-finals draw, with the Blaugrana taking on Paris Saint-Germain and Los Blancos taking on cross-city rivals Atletico Madrid.