Floored by a single punch from Rooney in a Manchester restaurant at the weekend, Gray felt the full force of the rage that Manchester United boss Sir Alex Ferguson is planning to unleash on Celtic in Wednesday night's Champions League showdown at Old Trafford.

The first competitive meeting between the two clubs could also see a return to action for Paul Scholes, who, like Rooney, has served a three-match ban as a result of a red card received in a pre-season friendly tournament in Amsterdam.

The pair are itching for a return to action, "like bears with sore heads," as Ferguson put it.

"They've not been happy bunnies and they're not satisfied unless they're playing," the Scott added. "They know they've been punished very unfairly but they're raring to go and it'll be great to have them back."

United's pre-Christmas exit from last season's Champions League was largely the result of their failure to score against either Lille or Villarreal at home.

But with Scholes now fully recovered from the eye problem that afflicted him last season and Rooney champing at the bit, Ferguson believes a lack of goals is unlikely to be an issue this season.

"It will be different this year I can assure you," said Ferguson. "If someone had told me this time last year we would finish bottom of our group, I would never have believed them.

"No one likes bad memories but good footballers should always look at situations like that and say 'I do not want that to happen again'."

Celtic have a good record against English opposition in recent years, having knocked Blackburn and Liverpool out of the UEFA Cup in 2001/02 and 2002/03 respectively.

But United will go into the match on the back of a four-match winning start to their Premiership campaign and buoyed by the memory of how they comfortably outclassed Rangers when they met the then Scottish champions in the group stages of the Champions League three years ago.

Even Celtic boss Gordon Strachan has admitted that this match may have come a little too early for his new-look squad.

New signing Thomas Gravesen however was upbeat about the Glasgow side's chances of pulling off an upset at Old Trafford.

"They are the kind of games you love to play as a footballer," said the Danish midfielder. "We can go to England with confidence and we will do our best down there.

"People think that the Scottish league is not so strong, but I think we can prove them wrong."

Dutch striker Jan Vennegoor, another of Strachan's new signings, admitted Celtic were far from the finished article at the moment.