Aston Villa boss Martin O'Neill has ruled out taking over as manager of Manchester United when Sir Alex Ferguson retires, claiming that whoever replaces the 68-year-old will have an "impossible job" on their hands.

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GettyImagesSir Alex Ferguson and Martin O'Neill will battle for the first trophy of the season.

Jose Mourinho is currently favourite to replace Ferguson when he stands down at Old Trafford - but many believe O'Neill would be a good choice for United. However, O'Neill said the idea of taking over as manager of the reigning Premier League champions has never entered his mind.

"I've never thought about that at all, not for one second, not even way back when I was at Celtic," he said.

"I think Sir Alex will decide, and I would think in about the year 2033 when he thinks to himself, 'yeah, I think that Champions League has gone past me for the final time', then I will have departed this earth long before him - because I've got a lot more worries.

"It's never really bothered me. And of course there's always somebody coming up, somebody whose name is relevant at the time.''

And O'Neill, whose Aston Villa side will battle against Ferguson's charges at Wembley in Sunday's Carling Cup final, believes whoever replaces Ferguson faces a tough job.

"For anybody it would be absolutely an impossible job to succeed him. What can you do? Win the Premier League 10 times? You'd still be just starting out against him.

"I know Brian Clough went to Leeds and said he could win it better but he only lasted 44 days and to be honest it wasn't his most inspiring moment.''