It is Jose Mourinho's 10-minute rule. Ten minutes. That is all it takes for the Chelsea manager to know whether a player is good enough. Whether a player can make it. Whether he has that desire, that hunger, that drive. Or whether he has to go. It is that ruthless.
"You know, I'm a coach," Mourinho says. "I'm not an office man and, as a coach, I think that the players must give confidence for me to say 'let's go'. Not the other way. The players and the agents would like this: 'Oh I need five matches in a row to prove myself.'"
Mourinho professes surprise. "Oh, you need five matches in a row? Oh, fantastic! You don't need five matches in a row. You need 10 minutes. In 10 minutes you can show me if you are ready or if you are not ready. (Kurt) Zouma didn't have five matches in a row."
The powerful, quick 20-year-old French defender follows the Mourinho edict. Zouma seized his opportunity and he has also shown that he has the stomach for the fight. Not just for Chelsea but to get into the Chelsea team.
It is an appetite that Mourinho feels other expensive young acquisitions lacked. Players such as Kevin de Bruyne and Andre Schurrle who were, perhaps, also not good enough?
"That's not true," Mourinho counters. "They are good enough. We have to sell them because they don't want to stay and compete for a place. That's the reason why you have to sell - not because they aren't good enough.
"What we don't want is to have players who are not happy to stay.
"You can ask them why they want to leave the club and if they're honest all of them - (Romelu) Lukaku, De Bruyne, Schurrle, (Mohamed) Salah - will say it's because they don't want real competition. They don't want to have some big players with them fighting for a place.
"I see, for example, Zouma the happiest boy to be in the squad, to be an important player like he is, to know that he has a brilliant future at this club, to know that John Terry is 34 years old and Gary Cahill is 30 or 31 (29). I see him always ready to play even in positions that aren't the best for him.
"Players are different and I respect the way they are and the club doesn't like to have unhappy people. When the players aren't happy, the club is normally willing to let them go."
But can Mourinho really tell in just 10 minutes?
"Yes, yes," he insists. "In 10 minutes it's difficult to score a Maradona goal - to get the ball in midfield, dribble 10 guys and score a goal - but that's not what you're expecting from a player.
"In 10 minutes you can show a lot. A lot. You can show you are ready, you are mentally ready, you are physically ready, you are ready to cope with the pressure, you are not the kind of guy that is ready to train and play against kids of your own age but not be ready to play at the high level. Ten minutes can say a lot."
Chelsea's Premier League title defence starts on Saturday at home to Swansea City.
"You have a minimum of five title contenders and the other teams get stronger and stronger," Mourinho says. "I think nobody can complain because everyone is investing - you go to Watford, you go to Bournemouth, Palace, Stoke, every club.
"Years ago the best players at the best teams in other countries left to come to the big clubs in England. (Now) in France they were complaining about (Dimitri) Payet and (Alexandre) Lacazette coming to England and saying that French football is losing players even to medium clubs. This is the reality.
"Southampton bought a Sporting Lisbon player (Cedric Soares), West Ham got a player from Marseille (Payet), Bournemouth got a top African player from St Etienne (Max Gradel), Newcastle got a big guy from Anderlecht (Aleksandar Mitrovic) and the Dutch boy who plays for the national team (Georginio Wijnaldum).
"Every club has very good players so I think it's difficult for the top teams in England because of the competitive nature.
"It's also difficult because they (other clubs) have players who could play in our teams - (Yohan) Cabaye could play for Chelsea, what's the doubt? Wijnaldum could play for Chelsea, what's the doubt? Gradel could play for Chelsea, what's the doubt?"
Mourinho was speaking at the Premier League's launch, at the Southfields Academy in London, amid the backdrop of 3G pitches funded by the club - just like other top-flight clubs - to encourage 11-to-19 year-olds to play the game.
The debate over giving opportunities to young British players has become increasingly vexed, given that flood of foreign talent. Mourinho has spoken about the prospects for Ruben Loftus-Cheek, the 19-year-old midfielder he has promoted to the first-team squad - but with a fierce public rebuke for taking "one step back" after a lacklustre performance on the post-season tour to Australia.
Mourinho stands by his criticism.
"Let's wait and see," he says curtly when asked whether Loftus-Cheek has learnt his lesson.
"People normally ask about chances and chances and chances and maybe that's a good excuse for the young players to be where they are. I think maybe for the good of English football, you should go the other way. Are you ready to get the chance?"
Are you ready to pass the 10-minute test? (© Daily Telegraph, London)
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