Former Real Madrid coach Radomir Antic is amazed at Cristiano Ronaldo's consistent scoring, calling the attacker "an alien".
The Portugal international has been in sublime form in 2013-14 and has already netted 25 goals in 24 Primera Division appearances ahead of Sunday's crunch clash with Barcelona.
"Cristiano is an alien and just keeps on scoring," Antic was quoted as saying by AS.
The 65-year-old warns that Barca face a tough task to get a good result at the Santiago Bernabeu in a Clasico that could have a huge say in the Spanish title race.
"It is a game where you always have to be at your best," Antic mused. "The majority of sides lose before they step onto the pitch.
"It's a type of pressure that's hard to explain."
Antic, who briefly worked at Barcelona in 2003, also offered praise for veteran defender Carles Puyol, who will leave Camp Nou at the end of the season.
"He is a boy who deserves all of my respect," he enthused. "He was one of the players I had under me who was always trying to improve himself."