John Utaka, left, joins Sulley Muntari for a lap of honour around Wembley following Pompey's victory over Cardiff Picture: Allan Hutchings

That is the admission from Pompey’s former boss, who recruited the Nigerian winger for a then club record £7m in July 2007.

Utaka would go on to supply the cross which provided Kanu with the FA Cup final winner against Cardiff in May 2008.

Yet despite a blistering start to life at Fratton Park, with two goals in his opening three matches, the former Rennes player never lived up to his billing.

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John Utaka, left, joins Sulley Muntari for a lap of honour around Wembley following Pompey's victory over Cardiff Picture: Allan Hutchings

And he was sold to French side Montpellier in January 2011 in a cut-price deal after amassing 13 goals in 114 Pompey appearances.

Redknapp said: ‘John Utaka was probably the one big disappointment we had.

‘He was a top player in France and had great ability.

‘He had days where he could rip you to pieces, he was quick and strong, played through the middle or played wide.

‘John’s Portsmouth career was up and down, though, it didn’t really hit the heights of the other lads, but he was a good lad, no problem.

‘He started off well. I don’t know what happened with John really, he was a good lad.

‘That sort of player is going to be up and down, he would have his days and others it didn’t come off for him. Those sort of players are like that, they can beat people some days and others it was difficult.

‘He was never going to be a 7/10 every week, either a 9 or a 4, that’s the way he played.

‘I used to get on him a bit, maybe too much looking back on it. I would get the hump with him sometimes, it happens with players sometimes.

‘But he played his part in the FA Cup final win, which you shouldn’t forget.’

Utaka registered on his Blues debut in a 2-2 draw at Derby on the opening day of the 2007-08 campaign.

Then, two games later, he netted against Bolton at Fratton Park with a stunning solo effort which tantalisingly suggested the Blues had themselves an outstanding talent.

Yet the Nigerian international’s performances could be frustratingly erratic and that proved to be his most effective Pompey campaign.

Redknapp lost confidence in Utaka and handed him just two more starts after the FA Cup final, both arriving in cup competitions.

The manager, of course, quit the Blues in late October 2008 to join Spurs, but the winger continued to be a peripheral figure for the remainder of 2008-09 under Tony Adams and Paul Hart.

Our interview with Harry Redknapp is part of our build-up to the 10th anniversary of Pompey’s FA Cup triumph.

Keep checking portsmouth.co.uk throughout the week to read more stories, while there will be a 16-page supplement in Thursday’s News.