In the week of Fernando Torres's birthday, it can't have been much of a present to see Didier Drogba back at Chelsea. The Ivorian's visit with his current club Galatasaray brought with it tributes from José Mourinho, hugs from his former teammates and misty-eyed pre-match reminiscences. All around Stamford Bridge banners still hang that proclaim Drogba as one of the greatest to wear Chelsea blue, and few fans would have begrudged the old warhorse one last goal at the ground. Torres must know that he will never be taken to heart in the same way.

He has always seemed to exist in Drogba's giant shadow. Though he was signed for £50m in January 2011, the sort of fee that should have ensured he was the first-choice striker, he made two less starts than Drogba during the remainder of the season, and the same number as Nicolas Anelka. His inability to cement the lone centre-forward spot Chelsea subsequently favoured always seemed to be coloured by the fact that, while Drogba was at the club, nobody else would be top dog – no matter what they cost.

Whatever Torres did, he always faded into Drogba's background. During Chelsea's successful 2012 Champions League campaign, he was outdone by the Ivorian in the most dramatic of ways. In the semi-final against Barcelona, it was Torres who sprinted half the length of the Camp Nou pitch to score the goal that made absolutely sure that Chelsea went into the final (and send Gary Neville on a viral journey around the internet). But Drogba, of course, scored the penalty that won the competition outright – and did so with his last kick for the club: an impossibly iconic slice of history that will forever dwarf Torres's contribution. It hardly helped, meanwhile, that Torres was not even allowed to take one of those spot-kicks.

But if an inferiority complex was the problem, it wasn't one that was solved after Drogba's departure. Torres has continued to frustrate and it is hard to fathom precisely why. If you ignore the price tag, his signing appeared to be an unquestionable piece of business. He was keen to leave Liverpool, a club he said was "in chaos" at the time. He was a proven goalscorer, one who scored a hat-trick within a month-and-a-half of his Liverpool debut in 2007 and another two – in successive matches – several months later. He scored 33 goals that season, 17 the next, and 22 in his final full season at the club – 65 goals in his 102-match, three-and-a-half season Liverpool career. Even for a club that lived to regret recruiting strikers such as Chris Sutton, Pierluigi Casiraghi, Mateja Kezman, Adrian Mutu and Andriy Shevchenko, Chelsea must not have had to think very long about signing him. But, though he has been in London for almost exactly the same amount of time that he was at Liverpool – three seasons and 103 matches, he has scored just 19 goals.

Torres has played under five managers at Chelsea, four of them Champions League winners, and the other a Europa League winner. But none of Carlo Ancelotti, André Villas-Boas, Roberto Di Matteo, Rafael Benítez or Mourinho could get Torres to play with anything like consistency. There were moments, brief reminders of a former life before another inevitable slump. After missing an open goal against Manchester United in 2011, there was the masterful swivelled shot against Swansea in the following match. A brace followed soon after in the 5-0 Champions League demolition of Genk in October. Villas-Boas proclaimed the striker's confidence was back and so he did not score again until March. When Benítez arrived at the club in November 2012, a temporary recruitment partly to rediscover the manager-striker relationship that once got the best out of Torres at Liverpool, he sparkled with seven goals in six matches in December. He then scored just three in the next three months – against Brentford, Boro and Steaua Bucharest. He did not score again in the league until May.

If coaches with that kind of pedigree – excusing, perhaps Di Matteo – could not get him to rediscover his form, then nobody can: the problem lies with the striker, not the staff around him. There are those who have pointed to the serious knee injury he suffered at Liverpool in 2010, claiming it robbed him of the pace that once served him so well. But Torres is hardly a slouch now, and he has had nearly four years to work a way around his problem.

There are arguments too that Chelsea do not suit his style of play. At Liverpool, the club would win the ball in their own half before Steven Gerrard would pass into space behind the opposition defence. Torres's speed would do the rest. But in Frank Lampard, Juan Mata, Oscar and Eden Hazard, Torres has hardly been short of world-class playmakers to feed him. And so his confidence is blamed instead – and that's a far tougher thing to quantify or resolve. If his inability to dislodge Drogba from Chelsea's starting lineup started his spiral of doubt, then the fact that his current manager seems to prefer the other ageing, iconic African striker of this generation – Samuel Eto'o – up front cannot help. The simple matter for Chelsea, though, is that they cannot afford to be sympathetic for much longer. For a club that sees itself as one of the best in the world, there comes a time for ruthlessness: and in Torres's case that time has long been up.

On the day that Torres turns 30, he has confessed an admiration for the Atlético Madrid manager Diego Simeone – currently in charge of the striker's first club and the one he has always held dearest. If Chelsea are wondering what to get Torres for his birthday, then granting him a simple transfer might spare them too much wrapping.