José Mourinho will remember it well. The 2007 Carling Cup final in Cardiff was only 12 minutes old when Abou Diaby slipped a pass across the edge of the penalty area and a whippet-fast teenager controlled it, nipped through a gap and finished adroitly past Petr Cech.

That player was Theo Walcott, it was his first goal for Arsenal and, although Mourinho and Chelsea would end up victorious, the promise of a boy still a few weeks short of his 18th birthday seemed undoubted. Arsène Wenger looked to have a brilliant young talent in his ranks.

Over eight years on from that game, Mourinho will take his Chelsea side to the Emirates to meet Arsenal on Sunday. In the intervening years Mourinho has left Chelsea, managed and won league titles in Milan and Madrid, returned to Stamford Bridge and is on the verge of more glory. It is unlikely Walcott will start the game. More than nine years since signing for Arsenal as a startled 16-year-old in January 2006, Walcott does not seem to be the finished article.

If the Southampton prodigy was blinded by the media glare when he was unveiled that day, it was merely a preparation for his even more surprising inclusion, four months later, by Sven-Goran Eriksson in England’s squad for the 2006 World Cup finals in Germany, despite Walcott not having played a single minute for Arsenal or in the top flight.

It is only one of the ironies of Walcott’s stop-start career that he has not made it to a World Cup since to reap the benefit of that experience, having been dropped by Fabio Capello in 2010 and then missing out injured last year.

It is perhaps another irony that Walcott, along with the permanently injured Diaby, who joined the club a week before him, are the longest-serving members of Arsenal’s squad. At 26 Walcott should be approaching his peak but remains a player who divides opinion among fans and pundits alike.

Walcott poses with the Arsenal manager, Arsène Wenger, after signing for the club as a 16-year-old in 2006. Photograph: Mark Thompson/Getty Images

It is not that his career has stagnated, more that a permanent state of inconsistency reigns. One moment he is burying a half-chance with undoubted finesse, the next he is back on the periphery, drifting through games, showing neither the required wit or aggression to combat the best defences in the Premier League and Europe. Discussions over a new contract have become a thorny issue for a player whose current deal expires in little over 12 months’ time.

Walcott and Arsenal have been here before – in 2013 his contract was within six months of finishing when he signed a new three-and-a-half year deal worth a reported £100,000 a week. Perhaps the signs of doubt from player and club were there then, some telling reticence to over-commit: the club’s customary five-year deal rule for a young player had not been adhered to and, modern contract negotiations being what they are, Arsenal must have known they would be back down this road soon enough.

Two years later and they are. Wenger’s treatment of the issue this time has been interesting, making a none too subtle dig at the player’s advisers last month. “He is very quick on the pitch but off the pitch not always,” said Wenger. Walcott then took to Twitter to say, quite pointedly, that no discussions had yet taken place.

So how badly do Arsenal want to keep him or, to be more pertinent, how much do they need him? Wenger’s 4-2-3-1 formation should suit the pace Walcott offers on the right flank but has ended up frustrating him. He has made no secret of his desire to play up front but as the lone striker he simply does not have the attributes, the ability to lead the line or the physical presence of Olivier Giroud or Danny Welbeck. Walcott inherited Thierry Henry’s No14 shirt and it was often felt he would follow the Frenchman’s footsteps in evolving from a wide player to a central striker too but that day still looks a long way off.

The arrival of Alexis Sánchez and Welbeck last summer to complement Mesut Özil, Santi Cazorla and Alex Oxlade-Chamberlain has merely intensified the competition for the wide roles at the Emirates. Sánchez has raised the bar of what is expected from Arsenal forward players, Giroud and even the slow-burning Özil have lately responded in kind. The defensive of industry of Sánchez, Welbeck and Oxlade-Chamberlain has also not gone unnoticed; it is an area where Walcott has often been found wanting.

Walcott scored his first goal for Arsenal in the 2007 Carling Cup final defeat by Chelsea. Photograph: Paul Ellis/AFP/Getty Images

The 2012-13 season had looked like it was to be his breakthrough year. With Robin van Persie having left for Manchester United, there was more of a goalscoring burden on others and Walcott responded, scoring 21 goals in all competitions. On the back of a goal at Euro 2012 for Roy Hodgson’s new-look England, Walcott, at 23, appeared to have arrived. Much like his lethal hat-trick for England in Croatia in 2008, however, it proved another false dawn, another moment when fleeting potential has not quite transformed into the consistent performer he craves to be.

Injuries have, of course, played their part. Persistent shoulder problems interrupted his early years at the club, and it took him until 2011-12 to have an entirely injury-free campaign. Theruptured anterior cruciate ligament that ended his season and World Cup hopes in January last year was an untimely blow, stunting tangible progress.

For his part, Wenger has been forthright he wants Walcott to stay. He has invested much time, and the club much money, into the player’s career and the prospect of his best years being spent elsewhere is not one the manager wants to entertain. He has seen that too often before. “He is only young and I believe he will have a great goalscoring record in the future because of the quality and intelligence of his game. Therefore I want him to stay with our club,” said Wenger last week.

That goal against Chelsea at the Millennium Stadium certainly feels a long time ago. Sunday would be a good time for Walcott to remind everyone of his attributes, maybe a few suitors as well as his own club.