Celtic insist they are not in negotiations with Roy Keane over a possible move for the former Manchester United midfielder.

The 34-year-old infamously left Old Trafford last week when his contract was brought to a premature end.

Celtic Park is known to be a favoured destination for the former Republic of Ireland captain and the Glasgow side quickly opened the door for possible discussions, which may start as early as tomorrow.

But, amid claims that the Scottish Premier League leaders have made contact with Keane, the club maintain any formal negotiations have not started.

A Celtic spokesman said: "Celtic have not, at this point, entered into contract negotiations with Roy Keane or his representatives."

Portsmouth and West Ham are the latest clubs to have voiced an interest in Keane. Manchester City, West Brom Bolton and Wigan are also monitoring the situation as the Cork man assesses his options.

West Ham manager Alan Pardew said: "I wouldn't dismiss it. I haven't explored what Roy wants to do because that is probably what is going to happen - it will be what Roy wants to do.

"But certainly I haven't closed the door on bringing a player of his stature to this club because that is the sort of player we want to look at.

"We have a great base here of young players, a good squad and a good spirit and to jump to the next level we need to bring in real quality players."

Earlier, Portsmouth chief executive Peter Storrie also admitted the Fratton Park club were looking at the possibility of signing the controversial midfielder. He said: "If we could bring Roy Keane to Pompey, it would be fantastic, but in what role I don't know.

"However, we are in a queue of about 40 clubs who have registered an interest with his lawyer. We would like to talk to him if he wants to talk to us. I am unsure whether Roy Keane wants to stay as a player or get into coaching."

Meanwhile, Manchester United's recent scoring record in the Champions League hardly inspires confidence ahead of their decisive match against Benfica in a fortnight - but Rio Ferdinand insists the team's strikers bear comparison with any in the world.

United know only victory in Lisbon will suffice if they are to make the knockout stages but they have not won away in the Champions League for two years and have scored only once in their last seven games in the competition.

Manager Alex Ferguson might be more concerned were it not for United's buoyant league form, and Wayne Rooney in particular continues to enhance his reputation almost with every match.

Rooney was a class above every player on the pitch during the goalless draw with Villarreal and Ferdinand is convinced that, with Ruud van Nistelrooy alongside the 20-year-old, United have little to fear in the Stadium of Light on December 7th.

Ferdinand said: "I don't think we would swap Wayne and Ruud van Nistelrooy for anybody in the world. Wayne can do almost anything he wants to do, he has had a fantastic impact here and that is there for everyone to see, and not just for Man United for England as well. The future looks very, very bright for him.

"Ruud is just a natural-born goalscorer and we wouldn't change those two for anybody - it's just getting a case of getting the rub of the green in the right areas."

Aston Villa are set to begin contract talks with Steven Davis in an attempt to fend off interest from United in the coming transfer window. The 20-year-old Northern Ireland international, who made his first Premiership start only 12 months ago, has been in outstanding form for Villa this season.

Davis signed a three-year contract last March but moves are already under way to extend that deal on much improved terms as reward for his progress.

United, who are understood to have watched Davis on several occasions this season, are likely to monitor the situation closely.

Ferguson is keen to add to his squad and Davis's profile would fit with the new generation of talent that the United manager is seeking to bring through.

Davis has yet to miss a game for Villa this season while his four goals make him the club's joint top-scorer along with Kevin Phillips. The Villa manager David O'Leary recently said that "if Steven plays well, so do we", but it was his display against England in Belfast on September 7th, when he set up David Healy's winner, that did most to raise his profile. The following month he scored his first international goal in the 3-2 defeat against Wales.

Davis's ability to break from midfield together with his quiet off-field persona have seen comparisons with United's Paul Scholes.