THE Flood gates have opened, in new Bhoy Willo's mind, at any rate.

The Irish international now knows precisely what it requires to cut it at a club like Celtic, and is the latest to discover that playing against either half of the Old Firm for a club like Dundee United is a million miles away from playing for them in world football's most hotly-contested derby.

Flood is not the first - nor will he be the last - player to come away from his first Old Firm game hoping he is not judged on that alone.

On a day of roller-coaster emotions, the fact he was selected ahead of Aiden McGeady would have put him on a huge high, only for him to come crashing back down after just 62 minutes to make way for the current Player of the Year.

But any feeling of disappointment in the pit of Flood's stomach would have been relieved on hearing manager Gordon Strachan congratulate him on his effort then go on to repeat that praise to the media immediately after the match.

Not that the dead-pan expression on Flood's face would give any clue. Just as the 23-year-old's hairline gives no real indication of his age, his poker eyes defy even Strachan to try and read what emotions lie beneath.

The manager is still trying to get to know the little man who turned out to be his biggest signing in the January transfer window. But he likes what he sees on the training field, and what he witnessed in that most daunting of all arenas in which to make your debut with every pass and step scrutinised via satellite across the globe.

Strachan would have liked the chance to test himself in such a match, so his admiration for those who come through it unscathed is clear.

He said: "Willo never gives his emotions away. He just sits there with the same expression. I can usually make people laugh, but I am not sure about him."

That's unnerving for Strachan who uses humour in many aspects of his difficult job; to get to know players; to defuse any nerves they be suffering; to get his point across without hectoring; to nurture team spirit and make it a happier place in which to get on with the very serious business of winning trophies.

Flood is very much still a challenge to the manager, in this respect. But even if the player is not smiling, the boss is when he considers how the new signing has pushed his way into his plans after only a couple of weeks on the payroll.

"I can't work him out yet, personality-wise, and it might take me a few months," said Strachan.

"He will have to get used to my sense of humour and coaching style. But he has been well looked after where he has been up to this point, and we will just try to help him settle in and make him even better.

"We all know what he can do from watching him play against us, and other teams like Rangers. But, trust me, it is a different thing actually playing for us.

"But I have watched him play with our players in training and decided, You are a good player whose energy we need.' "That was important at the weekend because we were aware that, especially early in the game, we needed to make sure we did not let Rangers score.

"We had to be on our guard against them counter-attacking us. We were a bit guilty of this as we were going for the game which didn't help us. So having someone like Willo who can get about the pitch quickly was important."

Flood is intelligent enough to know that many fans judge their players on what they produce in Old Firm games, the ultimate stage on which to become an instant hero.

His chance to make his mark came early when his cross picked out Scott McDonald, the scoring hero in the previous Old Firm game. But, from just six yards out, the Aussie couldn't convert.

The fact Flood was prepared to switch wings, take on Sasa Papac and deliver such a ball told his manager much about the new lad, and Strachan reflected: "He did well there because he had had a couple of rocky passes before then and he had come through that.

"I eventually took him off, not because I have a problem with his engine, which is good, but because we wanted to get Aiden on and Sami on as we were looking to win the game, and Willo does not have the best track record for getting goals.

"I could have taken Naka off, but we know he can produce a bit of magic, as he nearly did with his free kick in the final few minutes."

The big battle between Naka, Flood, McGeady and Maloney for the wide positions means there is a real danger of Celtic falling into the Subbuteo trap', especially with Scott Brown and Paul Hartley already towered over by the likes of Lee McCulloch at the weekend.

However, aware though he is for the need to keep an aerial challenge in the engine room, Strachan is not prepared to forego footballing principles for size.

He explained: "I could easily put a big team out there, but it is not the team I want to play.

"I would like to play an expansive style of football, but I know that is not going to happen in an Old Firm game.

"Which is why I have to ask my players to keep it tight and make sure the opposition get nothing to be excited about, then, hopefully, we can change it send on the guys with a bit of pace, which is what we did."