Alex Ferguson is convinced Rangers and Celtic will never get the chance to test themselves in the Premiership.

Three years after completing a Champions League double over Rangers, Manchester United boss Ferguson gets the chance to repeat the feat against the other half of Scotland's Old Firm at Celtic Park tonight.

Victory would sweep United into the knockout stage of the competition with a game to spare, although it will be no easy feat against a side who have lost just once - to Barcelona - in 11 previous matches on home soil in the competition.

'Battle of Britain' encounters of this magnitude inevitably see thoughts move to the possibility of Scotland's biggest two clubs testing their abilities down south.

And while Ferguson concedes the pair could succeed, he does not believe they will ever have the opportunity.

"Over the years there has been talk of British leagues," reflected Ferguson. "If the barometer of how successful Rangers and Celtic would be is the friendly games they play, they would probably do very well.

"But the situation is not as simple as that, and in any case the situation is all hypothetical because I do not think it will ever happen. It is too difficult a move."

With the Premiership's lesser lights unwilling to vote for a proposition which could cost them a place in the league, and the bigger fish anxious not to concede any of their power, the path to England is locked and bolted for the Glasgow giants, meaning European confrontations represent the only true measure of the respective standards.

United will start hefty favourites to gain the victory which would seal qualification and top spot in Group E with a game to spare. However, Ferguson is wary of the threat Celtic pose, particularly in front of the home side's supporters.

"Celtic Park is without question one of the best atmospheres anyone could experience and their players can be inspired by it," he said.

"If the game is going Celtic's way, you have your work cut out to stem the tide of emotion and enthusiasm that can be generated by that support. Celtic's record at home is one of the best in Europe, so we accept we are in for a tough game."

Even though Chelsea visit Old Trafford on Sunday in a top-of-the-Premiership showdown, Ferguson is promising no more than two changes to the side which beat Sheffield United last weekend.

One of them could see captain Gary Neville rested in favour of either John O'Shea or Wes Brown, with the Red Devils boss admitting his long-serving full-back may eventually require an operation to cure a worrying calf problem which has plagued him since returning from the World Cup.

"Gary came through Saturday's game OK and he trained on Monday but obviously, the injury has been a concern," said Ferguson. "We are holding our breath hoping it doesn't happen again because if it does we will have to take a long-term view and do something about it."