When does a temporary blip become a terminal decline? For the last two-and-a-half years, Fernando Torres has looked out-of-sorts, struggling to recapture the jet-heeled magic that made him one of the world's most-feared strikers.
After yet another tepid performance last night against Sparta Prague his lean spell extended to just one goal in 14 games.
Last season was a tale of collective triumph yet, personal toil for the Spaniard, who added the FA Cup, Champions League and Euro 2012 to his already impressive trophy haul despite making minimal contributions. Torres even ended the tournament in Poland and Ukraine as top scorer, although he was often sidelined as Vicente del Bosque experimented with a strikerless formation.
The very public nature of his fall from grace hasn't helped. Following a disinterested final few months at Liverpool, joining Chelsea didn't have the expected revitalising effect. After each misfiring week, laughs at the £50 million man's expense grew louder.
First, Carlo Ancelotti was the problem, then Didier Drogba, then the team's playing style. Roman Abramovich has steadily removed all these obstacles in order for his marquee signing to flourish, even incurring the wrath of supporters by instating Rafa Benitez as manager, but Torres looks no closer to playing as he once did.
Burnout has also been suggested as a reason for the spectacular drop in his performance level. Some footballers simply do have shorter top-level shelf lives than others, particularly those who rely as heavily on explosive pace as Torres has done.
At 28, he's beginning to seem that crucial-yard slower, not quite his usual responsive self.
This inevitably brings about comparisons to another former Anfield hero whose impact nosedived as the years wore on. In the late 1990s, Michael Owen emerged as the bright, young thing of British football, the teenager of boundless energy and potential destined to break all scoring records for club and country.
But his development was marred by injuries that many attribute to overplaying.
The career trajectory of Torres is similar.
An Athletico Madrid regular at 18, he went on to make 243 competitive appearances in six full seasons with his boyhood club.
Perhaps the physical effects of his playing style are finally taking their toll?
He certainly has an incredible number of miles on the clock for a player who should now be entering his prime.
Just as Owen had to adapt his game, so Torres may be forced to do the same. From playing off the shoulder and stretching defences in behind with blistering speed, Owen of recent times is a completely different creature. Instead he drops deep, involving himself more heavily in build-up play while retaining that poacher's instinct.
Whether Torres is prepared to sacrifice himself in this way, making the transition from self-serving world beater to tireless team man remains to be seen.