Rome (AFP) — When two of the world's best players face off in Wednesday night's Champions League final, the men charged with stopping Cristiano Ronaldo and Lionel Messi know there is no room for error.

Defending champions Manchester United will walk out at Rome's Olympic Stadium for Wednesday's show-case final to face a Barcelona side who have already humiliated European giants Bayern Munich and Real Madrid this season.

It promises to be a battle royal between two teams at the peak of their powers and includes a sub-battle between arguably the world's best two attacking players who can terrorise defences on their day.

United's Ronaldo currently has the upper hand having won both the world player of the year crown and the Ballon d'Or in 2008 while his side aim to retain their Champions League title by beating Messi's Barcelona side.

Dead-ball specialist Ronaldo hit a staggering 42 goals in all competitions last season, but his winner away to Porto and two at Arsenal in this season's Champions League campaign have gone some way to answering criticism of his big-game temperament.

Barcelona centre-back Yaya Toure admits the Spaniards can ill-afford to allow Ronaldo the freedom to control the midfield if they are to fulfill their ambition to win the competition they last claimed in 2006.

"They are physically very strong, they have a truly great footballer in Cristiano Ronaldo and they won the Champions League last year, so we know it will be very difficult," said the 26-year-old Ivory Coast international.

"It will be a great game and it's important that we play at 100 percent because anything less and you cannot beat this team."

While Ronaldo can strike fear into the heart of any goalkeeper with the deadball, Messi can give defenders nightmares with his ability to beat opponents with the slightest of touches from his favoured left-foot.

United defender Patrice Evra, 28, insists there is no special preparation for facing the Argentinian winger, but feels that coming up against the likes of Ronaldo and Wayne Rooney every day in training is adequate.

And the knowledge he would have to face the wrath of United manager Sir Alex Ferguson in the event of a poor display is an added incentive when dealing with Messi who came second in the voting for the world player of the year.

"Messi is a great player. I might stop him 10 times, but if on the 11th he goes past me and scores, people will say I have played badly against him," said the French international.

"I need to concentrate for all the game and win every challenge. Last year the boss told me I could win the game for United. I was very proud about that.

"The boss (Ferguson) trusts you but he likes to say things that will give you confidence. I don't want to disappoint him or my team-mates."

Ronaldo and Messi faced each other in last season's Champions League semi-final when Messi shaded the contest by proving the more dangerous of the pair although United progressed 1-0 thanks to Paul Scholes's wonder strike at Old Trafford.

United defender Rio Ferdinand looks likely to play in Wednesday's final having come through the weekend's training with no ill-effects on his calf injury which has kept him out for the last three weeks and Sunday's 1-0 win at Hull.

Jonny Evans, impressive at the back for United throughout the season, is on stand-by to partner Nemanja Vidic at the heart of United's defence in case Ferdinand fails to recover.

Barcelona star striker Thierry Henry and midfielder Andres Iniesta appear to have overcome their injuries after training on Monday.

Henry, who played against Barca on the losing Arsenal team in the 2006 final, has had a ligament problem since beating Real Madrid 6-2 on May 2, while Iniesta has been struggling with a thigh injury.

Barcelona coach Pep Guardiola has several options at full-back with first-choice pair Dani Alves and Eric Abidal both missing out through suspension.

Captain Carles Puyol and former United defender Gerard Pique are almost certain to start.

Meanwhile local authorities in Rome have issued a total ban on alcohol from 2200GMT on Tuesday to 0500GMT on Thursday in the Italian capital in a bid to prevent crowd trouble around the final with more than 67,000 fans expected.