Healy is a hard-tackling midfielder who loves to get forward and who has two good feet.
He scored twice during a 17-game loan spell with Coventry City last season.
He failed to force his way into the Republic of Ireland squad for the 2002 World Cup finals in Japan/Korea, even though then-manager Mick McCarthy wanted to call him up following the acrimonious departure of Roy Keane.
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World Cup red tape ruled it was too late to fill the void in his squad and Healy was forced to stay at home.
Healy joined Celtic from Irish club Wilton United five years ago and big things were expected but he has been unable to claim a regular place.
Sunderland and Aston Villa were both interested but the Black Cats could not come up with the compensation while Villa boss David O'Leary opted instead to sign Gavin McCann from, ironically, Sunderland.