Liverpool's Mamadou Sakho needs to prove himself after choosing to stay

Handing Jurgen Klopp a new six-year contract this summer was the biggest indication that Liverpool's American owners, Fenway Sports Group, would back their manager wholeheartedly, allowing him to do what he felt was necessary to get the club back to the top.

Since then, the Liverpool boss has laid down the law -- both stylistically and in terms of discipline -- at Anfield. Indeed, he's been ruthless in doing so. It is clear that if a player does not fit into his desired system they are to be shipped out.

Joe Allen departed Merseyside for Stoke City, despite arguably being Liverpool's best player towards the end of the previous campaign. Klopp wanted more physical presence and goalscoring from his central midfield, so out went the diminutive Wales international and in came Marko Grujic and Georginio Wijnaldum.

More important for Klopp, however, was removing players whom he felt were affecting the team spirit he has worked so hard to build.

Mario Balotelli, a player well known for causing disharmony throughout his career, was told early in the summer that he did not have a future at the club. He was not placed in the shop window in any of Liverpool's nine friendlies over the summer and was left behind to train with the under-23 side when the first-team travelled to the United States on tour. It was Klopp's way, or no way. Balotelli eventually left for French side Nice on transfer deadline day, with the Reds receiving no transfer fee.

On the U.S. tour, Klopp also banished another player who presented a threat to the harmony within his camp. Mamadou Sakho was a regular in the starting XI and a fans' favourite, but that didn't stop Klopp from acting.

After he almost missed the outbound flight to America, missed a treatment session on his injured Achilles, then turned up late for a meal, Sakho soon found himself on a plane heading back across the Atlantic alongside Brad Smith, a young left-back sent home to secure a loan move to Bournemouth.

"I have to build a group here, we have to start new here," Klopp said in California. "We have some rules and we have to respect them. If somebody doesn't respect it or somebody gives me the feeling he is not respecting it then I have to react."

Sakho's mind had clearly been elsewhere. He was suspended for 30 days by UEFA in April for failing a drug test after reportedly taking the fat burner Higenamine, a banned substance, but escaped further sanctions when UEFA confirmed it would not extend his punishment.

The Frenchman and his legal team maintained his innocence throughout the ordeal, believing Higenamine should not have been deemed a banned substance in the first place, but that didn't change the fact he was doing something outside of club rules as all players are required to consult the team doctor on consuming medication and supplements.

As a result, Sakho missed Liverpool's Europa League final defeat to Sevilla, a competition in which he played an integral role in, and, in addition, was left out of Didier Deschamps' France squad for this summer's European Championship in his homeland.

And, as the transfer deadline edged closer, it became clear that Liverpool wanted to send Sakho out on loan in order to get his career back on track. The club wanted him to prove his professionalism; Sakho did not agree with the Liverpool hierarchy's sentiments.

After turning down the chance to join Stoke City on a season-long loan, a source close to the club told ESPN FC that Liverpool gave Sakho an ultimatum: leave now to save your career. But the player did not heed the warning, going on to reject further offers from West Bromwich Albion and Turkish side Besiktas.

Now he is at Liverpool for another six months at least.

The club's summer business means that Sakho faces tough competition for regular game-time. On top of already established first-choice Dejan Lovren, the signings of centre-backs Joel Matip -- fully expected to be a starter -- and the veteran Ragnar Klavan from the Bundesliga have swelled the numbers. Even Lucas Leiva, now deemed to be a central defender by Klopp, is above Sakho in the pecking order.

Estonia captain Klavan was labelled "the most professional I have worked with" by his international manager, while Lucas, the club's longest-serving player, is seen as the perfect role model for youngsters.

Lucas is recovering from a hamstring injury sustained in the preseason and has only made a 45-minute cameo the U23 side so far this season. But in that game against Arsenal's youngsters at the Emirates Stadium last month, he showed what he can bring and ran the length of the pitch to celebrate one of 16-year-old Ben Woodburn's goals before motivating his teammates from the dugout in the second half.

"I've got to say, he is a real, real class act," U23 manager Michael Beale told ESPN FC afterwards. "He sat behind me and gave me feedback on the young players and what he sees. I would take a thousand Lucas Leivas, that's for sure."

So where does that leave Sakho?

After refusing to move on loan during the transfer window, time on the pitch and a long-term future at Anfield appear to be increasingly unlikely. It may be that he turns everything around and wins Klopp over, but if not, he only has himself to blame.