Most of the world's so-called best players have stepped up at this summer's World Cup finals. The likes of Lionel Messi, Neymar and Robin van Persie have all stood up and been counted over the past couple of weeks, much to the delight of the watching millions across the globe. But not every 'top player' has made a big impression. Chelsea-bound Diego Costa, for example, has been a complete disaster.
If Jose Mourinho suddenly had a few regrets about agreeing to spend £32 million for the Brazil-born Spain international, you wouldn't blame him. Costa had been identified by the Blues' boss as the perfect striker to fire Chelsea to titles next season after his stunning campaign with Atletico Madrid. However, big doubts remain about not only his ability, but also his mentality and ability to handle pressure.
ONE-HIT WONDER CONCERNS
Last season was the first time Costa had ever scored over 10 league goals in a single campaign. This isn't a 19-year-old prodigy we're talking about here: Costa turns 26 in October but only began to flourish as a striker during the 2012-13 season, when he scored 10 goals in 31 La Liga appearances while playing the role as back-up to Radamel Falcao.
When Falcao left, Costa suddenly burst into life at the Vicente Calderon, but nobody - not even Diego Simeone - expected the South American to be quite so prolific. That he managed to net 27 goals in 35 league matches came as a surprise to everyone - and perhaps even Costa himself.
Surely, then, there's a risk Costa may struggle to replicate his goalscoring exploits at a different club in a totally alien league. The striker has spent the majority of his professional career in Spain - hence why he controversially opted to represent La Roja instead of his native Brazil - and making the bold step to leave Madrid after, at last, finding a place to call home is an extremely courageous but dangerous move.
COSTA IS NOT CLINICAL ENOUGH
Despite his hugely impressive goalscoring record from last season, Costa spurned many good opportunities, including a fair few one-on-ones. All strikers miss chances, of course, but there were multiple examples of Costa lacking composure at key moments.
At Chelsea, every time he misses a gilt-edged chance, the comparisons with Fernando Torres will inevitably arise. Another expensive flop from Spain will be the accusation - and he will not have long to prove himself in England's top domestic league before the pressure really starts to build on his shoulders.
Most players need time to adjust to a foreign league - and Costa will be no different - but failure to hit the ground running will see him lose his place in the starting line-up to whoever else Mourinho manages to recruit this summer. Failure, therefore, is simply not an option.
QUESTIONS OVER HIS TEMPERAMENT
Costa has, in the past, been compared to Liverpool striker Luis Suarez. Not for his talent as a forward, but because of his unpredictable nature and gamesmanship. The Spain international is, for want of a better phrase, a dirty player. He will dive, antagonise opponents, harm opponents and generally act like a nuisance on the pitch.
He's the sort of player you want on your team, rather than playing against your team. But discipline is so important at the top level - and any early red cards will hardly improve his popularity and reputation.
Chelsea fans have only seen Costa play at Stamford Bridge once before - during last season's Champions League campaign - and they spent a portion of that game shouting obscenities at the striker after he took an age to re-spot a crucial penalty.
They got a small taste of what to expect from Costa that evening. But, as they discovered, he's no Didier Drogba and may not - contrary to what Mourinho believes - be the man to fire Chelsea to their first Premier League title since 2010 next term.