By Paul Fletcher

Manchester United take on holders Arsenal at Old Trafford in undoubtedly the most eagerly-awaited tie of the FA Cup fifth round.

The two best teams in England are set to battle it out for the Premiership, but only one will reach the quarter-finals.

United have already defeated Arsenal at Old Trafford this season, winning 2-0 in the league, but Arsenal will be confident of victory.

And there are sure to be several key contests during Saturday's showdown.

Rio Ferdinand v Thierry Henry

Arsenal hardly ever fail to score and Henry, the Premiership's leading scorer, is a major part of the reason why.

Henry is outstanding running at defences

As we saw during the match at Newcastle last Sunday, the Gunners are compact and solid in defence but explosive on the break.

Henry is simply imperious running at the opposition from deep and Ferdinand will have his work cut out to keep the France striker in check.

But Ferdinand's form has improved throughout the season and he has formed a solid partnership with Wes Brown.

The England central defender reads the game superbly - and will need to if he is to contain Henry.

Roy Keane v Patrick Vieira

No quarter asked and certainly none given in this potentially explosive encounter.

Keane is United's leader

The two captains, the two talismanic figures and the two players who will be doing more than anything to wrestle the initiative in the key central midfield area.

Both players are hugely motivated, strong in the tackle and amazing competitors.

It would take a brave man to decide which of the two is the more focused and whoever wins this battle will have won a decisive advantage for their team.

Mikael Silvestre v Robert Pires

Silvestre is one of United's most improved players and his form for his club has resulted in international honours for France.

Pires is tricky and quick

But he will have to be on his mettle against his compatriot Pires, who like team-mate Henry is a menace for the opposition with the ball at his feet.

Both players are extremely quick and it will be interesting to see how often Silvestre tries to push forward and force Pires into defensive action.

If he does, Pires may well fancy his prospects on the break, but then again to sit back and invite the Arsenal winger to push forward could be fatal.

It should be a fascinating duel.

Ruud van Nistelrooy v Sol Campbell

Van Nistelrooy may lack the explosive pace of Henry but his movement is excellent, his instinct for goal finely honed and he does not let much get in his way - which is where Campbell enters the equation.

Van Nistelrooy is committed and competitive

If Henry versus Ferdinand is about pace and touch, then the contest between Van Nistelrooy and Campbell will have a more physical dynamic.

The Dutch striker times his runs superbly and Campbell will have to maintain his concentration levels for the entire game.

Campbell is also the master of the last-ditch tackle, but anything late and it could be penalty time.

Sir Alex Ferguson v Arsene Wenger

This contest might not be out on the pitch but they are the best of enemies and as desperate as any player to win.

Jovial exchanges are few and far between

Ferguson's antipathy towards Wenger extends to the Scot moaning about the Frenchman's unwillingness to share a drink after the match.

Wenger's team hold both the Premiership and the FA Cup, but the latter could be wrestled from the Arsenal manager's grip on Saturday.

The United boss has already started to turn up the heat in the title race and he very aware of the value of putting one over Arsenal in the FA Cup.

Getting the tactics right will be crucial.