THE Old Firm game has been the making of Gary Hooper's reputation as a Celtic goalscorer but he's in an unusual place ahead of the season's penultimate derby at Ibrox.

With four goals from eight appearances in the most demanding domestic fixture of them all Hooper has proved his credentials at the level which matters above all in Glasgow. Yet his recent form has been drab. Hooper has gone from being frightening for Rangers to becoming a puzzle for Celtic.

He has scored in only four of his last 15 matches, although it's not the bare statistics which indicate his lost vitality and danger. Having scored 22 times in 36 appearances last season he is already on 20 from 40 this term, which is a poorer return but not to any significant degree. Even if he does not add any more between now and the end of the campaign he can claim to have done his bit in Celtic's march towards the league title. Twenty is the minimum requirement for any Old Firm striker and Hooper has reached that in each of his two campaigns.

But try squaring the Hooper whose exquisite first touch embarrassed Davie Weir when he scored in the 3-0 Parkhead derby last season with the one who lacked conviction and touch when he was given an early gift in Sunday's Scottish Communities League Cup final. It would have been a different day if he had buried the chance which was handed to him on a plate after only five minutes, when Mo Sissoko's suicidal pass across the face of the penalty area fell at his feet. A confident, on-his-game Hooper would have planted a first-time shot into the net or even rounded Cammy Bell and rolled home a finish. What he did instead, thumping an effort into Bell's body, reflected his underwhelming recent play. Other than playing a clever through pass from which Joe Ledley squandered an excellent chance at 0-0, Hooper was quiet.

He has been a resounding success for the £2.4m Celtic paid for him and his popularity among supporters is under no significant threat, yet the 24-year-old's performances can be unfathomable. When his game is off his touch looks heavy, the ball gets away from him, his passing is patchy and he drifts towards anonymity. Games can come and go without him making an impression. Defenders have to come believe that Hooper is one of those forwards who can be knocked off his stride early in a game.

He knows his form has dipped. In his last five games has not scored against Dunfermline Athletic, Aberdeen, Dundee United or Kilmarnock and even his winner against Motherwell felt unsatisfying for him. He didn't celebrate when he scored a winning goal against Stuart McCall's team last month because he had been so disappointed by his overall performance. "It was down to the way I was playing," he said when asked about looking unmoved. "I wasn't happy with that." The cup final was his 40th appearance of the season and 76th competitive outing for Celtic. Lately he has looked tired.

It's only a couple of months since Southampton were all over Celtic about Hooper. They bid once, twice, three times for him before eventually taking the hint when an offer believed to be worth close to £6m – and which would have almost trebled his £12,000-a-week wages – got them nowhere. Although it would be an exaggeration to say Celtic may now regret not taking that level of income when it was on offer for them, he's unlikely to attract that sort of sum in the summer unless his form improves again in the remaining eight Clydesdale Bank Premier League games and one or two Scottish Cup ties. Nor will his own bargaining position be quite so strong when he and the club sit down for the discussions about an extension which have been planned for the end of the season.

Hooper's four derby goals have made him a hammer of Rangers but manager Neil Lennon will be giving headspace to the idea of relegating him to a substitute's role at Ibrox. He hasn't been on the bench since the home game against Atletico Madrid at the end of November. His fitness should not be a problem, although he was removed from the cup final with 10 minutes left having suffered a dead leg. It's his flat overall play which is the issue. Anthony Stokes could be partnered instead by Georgios Samaras, or else Samaras – often favoured by Lennon in the derby – could be used up front on his own. Even Pawel Brozek, yet to start a match since arriving on loan from Trabzonspor in January, will see Hooper's current form as grounds for tentative optimism in the season's closing weeks.

What must feature prominently in Lennon's thoughts is the persuasive notion that Hooper troubles Rangers. He knows that the Englishman has hurt them before and could do so again, in an instant. It's another characteristic of Hooper's Celtic career so far that when his form and goalscoring falls away it can return explosively. He had scored only once in six games before bubbling up again to put two past Rangers last year. This season his goals have come in streaks. He went five matches without scoring and then found the net in eight of his next 12. That was followed by only one goal in the next seven.

Lennon will make the call on whether he might rise again in the Old Firm game. But going into the game, and for their own reasons, both clubs will have cause to be worried about Hooper.