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Mamadou Sakho can’t say he wasn’t warned.

It was prior to Jurgen Klopp’s first Premier League match at Anfield in October 2015 that the Liverpool boss spoke about the standards he would demand from the squad he inherited.

“I love to be something like a friend of the player, but not their best friend because a best friend understands everything,” Klopp said.

“If you are full of motivation as a player, if you are full of concentration, full of readiness and passion as a player, I’m not hard, I have open arms.

“If you are not, of course I am hard, but only because to work with players who don’t understand the professional part of this life, it’s a little bit of a waste of time.”

Sakho’s failure to embrace that “professional part” is the reason why in the space of eight months he’s gone from being a Kop cult hero to his manager confirming publicly that he has no future at Anfield.

There are many sides to Klopp.

There’s the beaming, charismatic man-manager who dishes out bear hugs to his players, and cracks jokes in press conferences.

There’s the passionate hive of energy on the touchline who loses his rag, whips the crowd into a frenzy, and celebrates goals with chest-beating and a flurry of fist pumps.

There’s the expert tactician with a keen eye for detail who spends hours with his staff poring over an opponent’s strengths and weaknesses, and drawing up battle plans.

Sakho’s situation shows another side. It underlines that for all the affection shown towards his players, Klopp isn’t a man to be crossed. He’s single minded and, when necessary, he’s ruthless.

The France international has discovered to his cost that if you break the rules and challenge Klopp’s authority then there is only one winner. It’s his way or the highway.

It was April 20 when Sakho made the last of his 80 appearances for the Reds. He scored in the 4-0 rout of Everton - a week after also netting in the miraculous fightback against Borussia Dortmund.

From that glorious high, things quickly unravelled. His world was turned upside down a few days later when he learned that UEFA were accusing him of a doping offence.

A damaging three-month saga ended with him being cleared in July but only after he had missed the Europa League final and Euro 2016 in his homeland as he served a provisional ban.

WADA’s case against him was so full of holes it was rightly thrown out but Sakho had tested positive for a substance called Higanamine – a compound found in a fat burner that Liverpool didn’t know he was taking.

All players are regularly warned they must not take anything without first consulting club medical staff. It all could have been avoided.

Sakho still had the chance to make amends in pre-season but he frittered it away with his antics at the Reds’ California training base. He was sent home for repeatedly breaking club rules as he riled the manager with his attitude.

Accusing the player of a lack of respect, Klopp revealed that Sakho was late for the team flight, late for a team meal and had failed to turn up to a treatment session.

Klopp prides himself on the team ethic and spirit and simply wouldn’t tolerate anyone damaging that.

The manager concluded that Sakho simply wasn’t worth all the hassle. With Joel Matip brought in to partner Dejan Lovren, and with Ragnar Klavan and Lucas Leiva as back-up, Klopp was happy with his centre-back options.

There was no way back for Sakho. He struggled to accept that initially, ignoring Klopp’s advice to go out on loan before the window shut in early September. Since then his daily routine has involved a session with the kids at the Academy. It’s a sorry state of affairs.

In January he will accept defeat and move on in a bid to relaunch a stagnating career. He should be full of regrets about what he’s thrown away.

His story should act as a warning to others that under Klopp nobody is bigger than the team.