Celtic completed the signing of Roy Keane on a free transfer on this day in 2005.

A month earlier, Keane had abruptly left Manchester United by mutual consent after his relationship with manager Sir Alex Ferguson deteriorated during a spell on the sidelines through injury.

Keane had been hurt in a challenge with Liverpool’s Luis Garcia in September of that year and grew frustrated while out.

Gordon Strachan and Roy Keane
Gordon Strachan pounced after Keane’s abrupt exit from Manchester United (Andrew Milligan/PA)

He had already clashed with Ferguson during the club’s pre-season training camp in Portugal, and then angered the manager with an MUTV interview in which he said he was open to finishing his career elsewhere as his contract ran down.

A further MUTV appearance in early November did even more damage as the United skipper gave a damning assessment of some of his team-mates’ performances in a 4-1 defeat to Middlesbrough.

In 12 full seasons with United, Keane had won seven Premier League titles, four FA Cups and the Champions League, but Ferguson was his usual ruthless self and, as tensions mounted, he cut ties as Keane’s contract was cancelled.

Gordon Strachan’s Celtic pounced as Keane joined the club he had supported as a boy – the midfielder signing an 18-month deal.

Soccer – Manchester United Press Conference – Old Trafford
Sir Alex Ferguson was ruthless in showing Roy Keane the door (Phil Noble/PA)

He would have to wait until January to make his debut, but it came in a shock 2-1 defeat to First Division Clyde in the Scottish Cup.

A month later, Keane scored in a Scottish Premier League win over Falkirk, which proved to be his only goal for the club.

After helping Celtic to win both the league title and Scottish League Cup, Keane retired that summer on medical advice.

The announcement came a month after he had returned to Old Trafford for his United testimonial, a friendly against Celtic in which Keane played 45 minutes for each side.