Keane completes Celtic switch Keane, the perfect present?

Both 34-year-olds prefer to play a holding role and Lennon has yet to agree a contract extension.

But Lennon said: "We are quite similar, but that was said about Paul Lambert and myself a few years back.

"I wouldn't envisage any problems with that at all. Roy has experience and will to win and, if he helps us win the title, he will be a great signing."

But former Celtic striker Charlie Nicholas has warned the arrival of Keane could signal a selection dilemma for manager Gordon Strachan.

"Stilian Petrov used to play wide right for Celtic and he hated the position," said Nicholas.

I think there could be a few problems Former Celtic striker Charlie Nicholas

"So I don't see how they can play Roy Keane and Neil Lennon together without moving Petrov to the right or the left and that is not suitable.

"So I think there could be a few problems and I will be very interested to see how it goes.

"Neil's contract is up at the end of the season and they're talking about another year.

"That might not come now with Keane signing for 18 months.

"People may ask how can we have two 35-year-olds sitting in central midfield."

Celtic chief executive Peter Lawwell denied suggestions that director Dermot Desmond had helped finance the signing.

But Nicholas said: "I think Dermot Desmond has pulled the strings on this one and has made a real issue about it.

"Dermot has not been very complimentary about the fans recently and he needed a little reaction back on his side - and this could be the one."

Former Celtic midfielder Paul McStay welcomed the signing.

"Any squad needs strengthening, especially if they are looking forward to Europe next year, where Roy's Champions League experience will be very beneficial," he said.

"I think Neil will welcome it. Good players want to play beside good players."

The secretary of the Celtic Supporters Association was also excited by the news.

"We know we are getting someone exceptional in British football," said Jim Divers.

"Everyone here in Glasgow - and fans around the world - is excited at the prospect of seeing Roy Keane in green and white hoops.

"Under Gordon Strachan, we are playing exceptionally well and have so many young players coming through.

"Keane is a master on the training pitch and can pass on his experience."