Former Manchester United star Henning Berg believes Celtic have a 'one-in-10 chance' of pulling off an Old Trafford shock in tomorrow's Champions League 'Battle of Britain'.
The Premiership leaders are red-hot favourites to sweep aside the Scottish giants in their Group F opener.
But Berg, who knows what it is like to win the competition after his heroics in 1999, believes Celtic must hold on to the slim hope everything will go their way.
Berg said: 'If Celtic frustrate United and they defend really well then they have a chance of getting something.
'Even if United were playing the worst team in the world, they could lose against a team because of bad luck. United would win nine times out of 10 but that one-in-10 chance is what Celtic will be looking to exploit. Patience is key.'
Berg, who was on the receiving end of a 3-0 defeat at Old Trafford when Rangers visited in the same competition in November 2003, believes midfielder Thomas Gravesen is vital to Celtic's midweek plans.
The new signing from Real Madrid is convinced his team-mates can spring a surprise.
Gravesen enjoyed a decent debut against Aberdeen on Sunday and Berg, a Champions League winner with United in 1999, knows how important the Dane will be for Gordon Strachan's men.
'Thomas is so crucial for them as he will know perfectly well what to expect in this game,' said the Norwegian.
'He has played in England before with Everton and has played in the Champions League and also in World Cups and European Championships with Denmark.
'His experience will help his new team-mates and [he] will be making sure everybody is in the right position to defend.
'He will make them defend as a unit and make them compact. It is important they don't give United any space.
'He is a ball-winner and can play a bit but he must curb his enthusiasm and be disciplined if Celtic are to do well.'
A young United side swept aside the Hoops at Parkhead in July and Lou Macari, who played for both teams, believes that woke Strachan and his board up to the fact they had to make signings ahead of club football's greatest competition.
Macari said: 'Although Celtic lost 3-0, it could have been five or six and United were well below strength.
'That was a wake-up call to the manager and the board and showed them they had to strengthen.
'Gordon must have known then his team were no way good enough for the Champions League. Signings were essential.
'Their team was good enough for the Scottish league and they proved that by beating Kilmarnock 4-1 but they knew they needed to make signing for the Champions League.
'That Celtic team were more than capable of winning the SPL but in Europe it was well short.'