Yet he felt like a part of the Glasgow side for only a few weeks, a dearth of opportunities in the first team causing the Dublin-born midfielder to feel distant from a club he had agreed to join on a two and a half year contract. "I was never a Celtic player," he said yesterday.
For the 28-year-old, the experience of being at Celtic was quite meaningless, then - a change of management when Gordon Strachan was replaced by Tony Mowbray made sure of that - and by the end he was pleased to leave it all behind him and head for the npower Championship and Middlesbrough.
Yet, there is no bitterness from Flood, now plying his trade at Aberdeen and in place to take on with Celtic again when the champions visit Pittodrie this afternoon. Rather, there is an acceptance that, in the end, it is the assessment of a manager which will determine your future.
"I never played really, so I didn't consider myself a Celtic player," said Flood, who scored his first goal for Aberdeen on the opening day of the league season against Kilmarnock. "Football is about opinions. Gordon Strachan [who signed him from Cardiff City] really liked me as a player and I have a lot of respect for him as he made me a better player. But when Tony Mowbray came in, I wasn't one of his signings and he had his own ideas.
"I'm disappointed I didn't get to play as many games as I would have wanted. When you are training all week and not playing on a Saturday it makes no difference whether you are at Real Madrid or Red Bull Rovers - if you don't get a game there is no point being there."
Flood has shown an edge in the opening two fixtures of the season to help the Pittodrie side set an impressive tempo, winning matches against Kilmarnock and Motherwell. There is a renewed belief within the Pittodrie club and the Irishman can envisage success this season
"We have a bit of drive, pace, nastiness, killer instinct in front of goal, a good defence, decent goalkeepers and good competition for places," he said. "But there is a long hard season ahead."