Tottenham Hotspur star Dele Alli was once one of the most valuable youngsters in world football.

In 2018, a study conducted by CIES Football Observatory concluded that the Englishman was the most valuable midfielder in the world, ahead of the likes of Kevin De Bruyne, Paul Pogba and N'Golo Kante.

Just a year earlier, former Spurs boss Martin Jol claimed Alli wasn't too far off being a £100m player, as per football.london, and that was reflected by Transfermarkt at the turn of 2019, where they valued the attacking playmaker at a whopping £90m.

Value plummeting

Things are vastly different now.

CIES' latest update (8th March 2021) sees the 24-year-old valued at just €30m (£26m), which emphasises just how drastic a downfall he has had in recent seasons.

By comparison, Manchester United's Bruno Fernandes is now the most valuable midfielder at an astonishing €151.1m (£130m), with Chelsea's Kai Havertz closely following behind at €136m (£117m).

Alli has never been one to be overhyped, but his increased exposure at the elite level since a £5m move from MK Dons aged just 18 has levelled out the public's expectations of him somewhat.

But what are some of the factors behind his seismic collapse?

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False dawn under Mourinho

After Mauricio Pochettino was sacked in November 2019, the arrival of Jose Mourinho handed Alli an opportunity to reinvent himself - to shake off that annoying tag of 'Dele's brother' often showing up rather than the player himself.

Indeed, this looked to be the case almost instantly, as a reinvigorated Alli delivered three goals and three assists in the first four matches under the 'Special One' but that would upturn in form turned out to be ever so short-lived.

Since then, Amazon's 'All or Nothing' docuseries has come out, and there's a clip of Mourinho calling Alli "lazy" but in more colourful language. As a result, the Pochettino favourite has only played 964 minutes in all competitions this season, of which 11 of 22 appearances have been starts, via Transfermarkt.

A move to Paris Saint-Germain, the new home of the Argentine boss, fell through in January and now he cuts an often isolated figure in the Spurs team or more so, on the Spurs bench.

Out of England reckoning

With a lack of game time and consistent performances, comes a consequence at international level - unless you're called Jordan Pickford or Eric Dier.

Having racked up 37 caps for England, Alli was axed from Gareth Southgate's squad for their Euro 2020 qualifiers and hasn't actually been seen since their UEFA Nations League third-placed playoff win over Switzerland in July 2019.

It'll come as a bitter blow to Alli that he won't be involved in a major tournament this summer but given his age, he has every chance of salvaging his Three Lions career in time for the Qatar World Cup.

He could take a page out of Jesse Lingard's book after the West Ham loanee earned his first call-up since the very same game.

Where now?

It wasn't too long ago that Alli managed a whopping 31 direct goal contributions in one season (2017/18) and at just 24 years of age, he is still nowhere near his peak.

Around this time, he was being lauded as a "competitive animal" and a "freak of a talent" - also drawing lofty comparisons to the likes of Steven Gerrard and co.

Now the forgotten Spurs man has only contributed towards seven goals, which is still respectable considering the lack of minutes on the pitch.

Though he may well need to force an exit this summer and Spurs chairman Daniel Levy ought to cash in before his value sinks even further under Mourinho.

AND in other news, Spurs handed Sergio Reguilon transfer boost...