Captain David Beckham warned Wayne Rooney and his England team-mates of the need to be careful off the pitch amid a police investigation into an alleged assault involving the teenage striker.

Beckham believes Rooney, 19, has matured significantly since moving to Old Trafford last summer but still cautioned against the potential pitfalls of life in the public spotlight.

Greater Manchester Police have confirmed they are launching inquiries into claims by a 22-year-old student that Rooney struck him during an argument in a Manchester city-centre bar on Monday night.

Rooney, who was yesterday training with the England squad, has been reassured his place in Saturday's World Cup qualifier against Northern Ireland is not in jeopardy, even if he is charged by police.

Beckham said: ''It is hard as Wayne is a young player, he's gone out for dinner and there has apparently been an alleged incident. But these days we have to be careful.

''There is obviously a spotlight on professional players and there has been for a few years now.

''I'm not talking about Wayne in this sense, but if you don't conduct yourself in the right way, then you look bad and you're made to look bad.

''It's important that players look after themselves and behave themselves.''

Beckham nevertheless believes Rooney, who has already endured considerable controversy in his short career, is learning his responsibilities.

''For me, Wayne has improved since he's been at Manchester United. I think he's been exceptional,'' he added.

''Even on the pitch, he's grown up a lot and his performances at United have been incredible.

''He's a young player, he is going to go out with his friends and girlfriend and there are going to be incidents but as long as he's playing his football, that's where he's most comfortable.

''When he first went to United, I said he was going to the right place and had the right person (Sir Alex Ferguson) looking after him. That shows by his performances on the pitch and the way he is off the pitch as well.''

Beckham rejected any idea Rooney had affected his preparations for Saturday's qualifier by going out late on Monday night with United team-mates, including Rio Ferdinand.

''I don't think there's a problem with that on a Monday night if there's a game on the Saturday. If you're going out on a Thursday night then that's a problem,'' insisted Beckham.

''If it (the ensuing controversy) affected him, it would be down to me or some of the experienced players to talk to him but judging by the way he is, he's not down about anything.''

Rooney's place in the England qualifiers against Northern Ireland and Azerbaijan will nevertheless not be in danger.

The Football Association's rules have changed since Alan Smith was asked to leave the squad before a friendly against Denmark in November 2003 after simply being interviewed by police.

Their policy in cases now is to only consider suspending players from England duty if they are found guilty of an offence.