Liverpool goalkeeper Jose Reina has warned Barcelona that Manchester United will 'kill' them if they show any fear in Wedneday's Champions League final.
Rafael Benitez's men were the only team to do the double over United this season, brushing them aside 2-1 at Anfield before demolishing them 4-1 at Old Trafford.
And Reina feels that Barca can do the same if they take lessons from United's bitter rivals.
"It's not easy to beat United," he told Spanish newspaper Sport. "The key is to approach them head on.
"You can't go out there with a heavy heart nor with fear, because if you do they'll end up killing you. That's what we did.
"United suffer when they don't have the ball, like Barca. To beat them you have to dominate possession and play without fear, with nerve.
"But I'm not the one to say it, (Barca coach Pep) Guardiola knows better than anyone what to do and how."
Barca are on the verge of completing an unprecedented treble and Reina has been impressed by his former team's stunning season.
However, he has warned the Catalan giants they face the toughest of tests against United, looking to become the first team to successfully defend the Champions League.
"Barca have been spectacular this season," he continued. "The numbers speak for themselves.
"To win the Copa del Rey and the Primera Division, and moreover in the manner they did, shows how phenomenal everyone has been.
"Let's hope they win the Champions League now, it will be an historic treble."
He added: "Much is said about United's attack, but the key is the defence. They have let in very few goals this season in the Premier League - 24 in 38 games. And they won it.
"In Europe they have also been magnificent. They play as a block, dominating all areas of play. And they are very complete. They also create danger in counter-attacks, dead-ball situations...they have everything."
Although he predicts a 1-0 victory to Barca, Reina admits it is difficult to pick a winner.
"I want Barca to win of course," he said. "But it is a very equal final and difficult to predict.
"The two teams are very similar. They have similar styles, the both use attacking football, they dominate possession, and their statistics have been very good.
"For that reason they have both won their respective leagues."
Reina progressed through the ranks at Barca and spent two seasons in the first team before leaving for Villarreal in 2002.
The Spain goalkeeper moved to Liverpool four years ago and although he admits he would love to return to the Nou Camp, he insists he is happy at Anfield for the time being.
"Any footballer would love to play at Barca," he added. "Knowing it as my home, it would really excite me, but my place now is at Liverpool, where I feel very comfortable.
"Moreover, Barca already have a great goalkeeper. Victor Valdes has had a great season and if Barca have reached so far, also in the Champions League, it's because of his good work."