Celtic have completed the signing of former Manchester United captain Roy Keane, with the midfielder initially signing a deal that will run until June 2007.

Keane, who ended his Manchester United career last month by 'mutual consent', was linked with Real Madrid earlier this week.

But, when the Spanish giants cooled their interest in the 34-year-old Corkman, Celtic seized their chance.

Keane's deal is believed to be worth £40,000 a week. The midfielder will be eligible to make his Hoops debut against Clyde on January 8, when Celtic take them on in the Tennent's Scottish Cup third-round.

Hoops chairman Brian Quinn made it clear his club would not be able to come close to matching Keane's United wages, believed to be £90,000 a week.

Italian sides Juventus, Roma and Fiorentina were at various points linked with the player, while Manchester City boss Stuart Pearce admitted any club in the Premiership would be happy to have a leader like Keane in their ranks.

Latterly Everton and Bolton Wanderers emerged as contenders, their cause aided by the fact that moving there would allow Keane to stay in the north-west, but Real Madrid seemed favourites when a club spokesman revealed he was 'on a list of possible signings' earlier this week.

However, Real president Florentino Perez offered a cooler response, insisting transfer targets would not be discussed until the club had completed their 2005 Primera Liga fixtures.

The saga has now moved full circle, with Keane sealing a move to Parkhead today.

It was originally thought the 34-year-old would have been lined up to make his debut at Hearts on January 1.

But the Scottish Premier League insist Keane will not be registered in time and his debut will have to wait until the Tennent's Scottish Cup third-round tie at Clyde on January 8.

An SPL spokesman said: "If players want to be registered for that weekend's fixture, they must be registered by 5.00pm on the preceding Friday as the registration window is not open that day.

"So players are ineligible to play on December 31, January 1 and 2 unless they are a free agent outside of the transfer window."

He continued: "However, this wouldn't apply to Roy Keane as he has been registered with Manchester United, but the club has been informed of that fully."