West Ham United’s £100million summer transfer splurge was met with a mixed reaction. Some felt ambitious and astute acquisitions were made. Others decried the Hammers’ hubris and a more-money-than-sense attempt at bridging the gap to the Premier League’s top six.

But the fact one of their new recruits, just four months after arriving at the London Stadium, is now reportedly being targeted by Paris Saint-Germain for double the fee West Ham paid for him suggests, somewhere along the line, their recruitment drive went very right.

Issa Diop, a 21-year-old centre-back, was signed from Toulouse for £22million in June, briefly a club-record fee.

The Hammers went on to make a handful of more attention-grabbing purchases, such as the captures of Felipe Anderson from Lazio for £35million, Andriy Yarmolenko from Borussia Dortmund and Jack Wilshere on a free from Arsenal, but the young French defender represents the club’s most astute piece of business from this period.

Captain of Toulouse, a France under-21 international and a European champion at under-19 level in 2016, Diop had been on the radar of several major clubs for some time. There was still a perception, though, especially given Toulouse’s struggles in 2017/18, that he remained a little unrefined, needing to further develop in some key areas before he’d be ready for a big move; and before he could justify the kind of fee West Ham paid.

As such, there were misgivings over the Hammers’ decision to make Diop their marquee defensive arrival of the 2018 summer; most reviews of their business upon the window closing in August suggested their squad had been left top-heavy, with plenty of attacking talent but dangerously short of quality at the back.

But Diop’s form, alongside fellow impressive summer signing Fabián Balbuena and with sought-after teen Declan Rice in a protective midfield role, is beginning to turn West Ham’s perceived defensive weakness into a strength.

Diop could have been forgiven for requiring a period of adaptation to the Premier League, given his age and relative inexperience. His assimilation has been instant, though, with his performances marked out by calmness in possession, confidence and the sublime timing of tackles one would associate with a seasoned veteran.

He ranks among the top 25 Premier League centre-backs when it comes to interceptions per 90 minutes, and is in the top ten for tackles per 90. More impressive still has been his assuredness with the ball, which sees him rank 21st for both open-play key passes and successful take-ons per 90. He is unafraid to stride forward in possession and connect with his attacking colleagues.

No West Ham player with more than five league appearances this term can match Diop’s passing accuracy (87.6 per cent), too. The Hammers recruitment department knew, surely, they were getting a young defender of sky-high potential, but even they could not have expected the 21-year-old to appear so close to the finished article this soon.

Diop’s display in West Ham’s 3-1 win over Manchester United at the London Stadium in September even drew praise from opposition manager José Mourinho, who labelled the Frenchman a “monster” for the way the 6ft 4ins centre-half authoritatively kept the Red Devils at bay.

“[He had a] fantastic match,” the United manager told BT Sport. “Congratulations to the scout that found a 21-year-old kid Diop – a monster who dominated in the duels.”

Now, with just ten West Ham outings to his name, Diop has caught the eye of Ligue 1 champions Paris Saint-Germain, according to the Daily Mail, with reports suggesting the Champions League contenders are ready to fork out as much as £50million to sign the defender.

While that would represent a quick and significant profit on the Hammers’ investment, if they are serious about building towards challenging the Premier League’s established elite, they must resist all offers for Diop at this stage.

The pull of Paris will be hard to ignore for the Toulouse-born player, should PSG’s reported interest be backed with a firm offer. But the onus is on West Ham to convince the youngster that, for the time being, staying put is the best move for his development; they must also assure Diop their grand plans will result in Champions League football within an enticingly short, yet realistic, timescale.

Currently 13th in the Premier League, averaging under one point per game, that seems a long way off, and West Ham‘s record summer spending has not yet proven as fruitful as hoped. But in Diop, they have unearthed a gem, one that must be kept, rather than cashed-in on, if they are serious about breaking up the ‘Big 6’.