David Beckham is refusing to fall into the trap of writing off Anderlecht's chances of causing an upset against Manchester United in their opening Champions League game at Old Trafford tonight.

The England midfielder has warned his team-mates not to take it easy in the first group stage of the Champions League and get caught out.

United players feel they failed to retain the European Cup last season because they struggled to reach their best form in the opening games. The malaise carried on into the later stages of the competition and it was clear during their quarter-final defeat by eventual winners Real Madrid they were not at their best.

"We won't underestimate anyone this time round. Anderlecht will be a good team because they have made it into the Champions League," said Beckham.

United have poured thousands of gallons of water on to the pitch in a bid to ensure key defender Jaap Stam can play.

The Dutch international defender has an Achilles problem brought on by the hard ground in the early part of the season and manager Alex Ferguson has ordered the pitch to be soaked so he can pit Stam against big Anderlecht striker Jan Koller.

United are without winger Jesper Bloomqvist through injury and Quinton Fortune who is with South Africa's Olympic squad. They also have a doubt over Dwight Yorke because of a hamstring strain.

Anderlecht coach Aime Anthuenis is more concerned about tactics than injuries. He is expected to keep to the 4-4-2 line-up that has brought four wins from five league games in Belgium but has hinted he may switch to a five-man defence with Davy Oyen man-marking Beckham.