The Portugal international has been in stunning form in 2013-14, scoring 41 goals in 37 appearances in all competitions, and Mascherano has warned his teammates that they cannot afford to give the prolific attacker any space.
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"Cristiano is an extraordinary player who has won the Ballon d'Or for that exact reason. He can score a goal from out of nowhere," the versatile Blaugrana defender told Goal. "He has a lot of quality and a tough job awaits when we face him. It will be hard to stop him and I hope that he will not be at his best on Sunday.
"We will try to keep him on a tight leash and not give him any space, but he's the kind of player who can still hurt you even if you mark him tight. In the end, players like him are among the best in the world. With Ronaldo, his goals are often the result of his ability rather than of defensive mistakes."
Nevertheless, Mascherano has insisted that Barcelona possess an even bigger threat in Lionel Messi.
"Leo just keeps improving his own records," the 29-year-old said of his fellow Argentine. "We are talking about a player who has marked an era. He will continue to score goals in the years to come as he is still young.
"It's hard to find words to describe Leo. Every positive word seems to have been used already to praise him. Is he better than [Diego] Maradona? It's all subjective because everybody looks at things differently. I think that Leo has shown a lot of things. I don't like to compare them as they played in different eras. All I can say is that Leo is the best player I have seen in my life."
The versatile defender then went on to discuss this weekend's Clasico and made it clear that Barca prefer to do their talking on the pitch rather than make bold claims in the build-up to the game.
"You don't say that you're superior," the former Liverpool midfielder argued. "You have to show these things on the pitch. We have to go out there and win in order to show who's best. Madrid currently top the table and it's up to us to give our best. We must realize that it's a final for us and need a great day.
"There are no guarantees going into this game. We have lacked a certain consistency in 2014 that we did have in previous years."
Barcelona beat Madrid 2-1 at Camp Nou earlier this season but heads into this weekend's fixture at the Santiago Bernabeu third in La Liga, four points behind the table-topping Blancos.