For most clubs, producing a starting XI worth over £300million from their academy alone would be heralded as a phenomenal success.

Unfortunately for Manchester City that talent has made a combined total of just 92 appearances for their first team - 64 of which were made by Leicester striker Kelechi Iheanacho alone.

While Pep Guardiola's gilded squad have just landed an unprecedented domestic treble, behind the scenes one of the country's best academies is haemorrhaging its best prospects.

Dortmund's Jadon Sancho is one of the hottest properties in world football right now

The £100m-rated winger came through Manchester City's youth academy before quitting

Brahim Diaz is now at Real Madrid having also graduated from City's academy

Like many young players, Diaz decided he had a better chance of playing if he left City

Since the club's £200m state-of-the-art youth and training Etihad Campus opened in 2014, Monaco playmaker Rony Lopes, Bournemouth starlet David Brooks and England prodigy Jadon Sancho are among those who have slipped through City's clutches.

It has proved costly. Brooks, recently voted Welsh Player of the Year, was let go at the age of 16 for being too slight. He joined Sheffield United for nothing, and is now worth around £25m in the current transfer market, although there have been reports of a bid as high as £50m incoming from Tottenham.

Lopes, meanwhile, was sold for a little under £9m, and is now thought to have a market value around three times higher. Sancho has been linked with a move to rivals Manchester United for more than £100m - 10 times the fee Borussia Dortmund paid for him in 2017.

Often, when a player is released it's simply a case of misjudgement. Brooks offers a clear example of this, and so does Kieran Trippier, who was let go by City seven years ago as it seemed unlikely he would ever displace club legend Pablo Zabaleta. City are also not the only side to have condemned a diamond in the rough to the scrapheap.

But it is Sancho's exit, coupled with the January departures of Brahim Diaz and Rabbi Matondo to Real Madrid and Schalke respectively, that tell an altogether different - and perhaps more troubling - story.

All three players were offered contracts to stay, but chose not to sign.

The circumstances of Sancho's exit are well known. He was offered the chance to become City's best-paid academy player ever. He rejected the offer.

A year-and-a-half later, the Londoner has won his first England caps, demoted Chelsea's £58m acquisition Christian Pulisic to the subs bench at Dortmund and topped the Bundesliga assists charts with 15, adding 12 goals to boot. He is becoming one of the most coveted players in world football.

Rony Lopes is now flourishing at Monaco, having made his way through the ranks at City

Lopes looked set for a bright future at the Etihad Stadium during his first few games for City

David Brooks is now building his reputation at Bournemouth and is attracting big clubs

Brooks was another kid who left City to find more first-team opportunities elsewhere

Diaz and Matondo followed suit during the winter transfer window and they too rejected the chance to stay. But Sancho was not starting a new trend; in fact, these three players are only the latest to follow a steady stream of youngsters pointedly choosing to leave the club to better their career prospects.

In 2016, promising forward Rafael Camacho chose to leave City for Premier League rivals Liverpool instead. That same year, Tyrese Campbell - like Sancho - shunned a new contract to join Stoke City.

Twelve months later, Lopes left the club for Monaco in confusing circumstances - as Manuel Pellegrini had publicly asserted the 19-year-old would only leave on loan. Just hours after Pellegrini had spoken to the media, it transpired that Lopes had jumped at the chance to leave permanently.

Last summer, Steven Gerrard's cousin, 17-year-old Bobby Duncan, walked out on City as he had become frustrated with a lack of opportunities. He followed Camacho to Anfield, having been with City since the age of 10.

It is clear that a concerning number of City's best youngsters are trying to jump ship, rather than attempting to break through the club's 'grass' ceiling.

SALES OF EX-YOUTH PLAYERS BY CITY UNDER GUARDIOLA... £25m - Kelechi Iheanacho (Leicester) £22m - Brahim Diaz (Real Madrid) £13.5m - Angus Gunn (Southampton) £12.5m - Enes Unal (Villarreal) £12m - Jason Denayer (Lyon) £11m - Rabbi Matondo (Schalke) £9m - Jadon Sancho (Dortmund) £9m - Pablo Maffeo (Stuttgart) £5.5m - Angelino (PSV) £4.5m - Olivier Ntcham (Celtic) £4m - Seko Fofana (Udinese) £4m - Bersant Celina (Swansea) £1.5m - Tyrese Campbell (Stoke) £700,000 - Rodney Kongolo (Herenveen) £200,000 - Bobby Duncan (Liverpool) TOTAL = £134.4m Advertisement

...AND THEIR CURRENT APPROX. TRANSFER MARKET VALUES £15m - Kelechi Iheanacho (Leicester) £22m - Brahim Diaz (Real Madrid) £15m - Angus Gunn (Southampton) £12m - Enes Unal (Villarreal) £27m - Jason Denayer (Lyon) £11m - Rabbi Matondo (Schalke) £100m - Jadon Sancho (Dortmund) £7m - Pablo Maffeo (Stuttgart) £11m - Angelino (PSV) £4.5m - Olivier Ntcham (Celtic) £11m - Seko Fofana (Udinese) £3m - Bersant Celina (Swansea) £300,000 - Tyrese Campbell (Stoke) £500,000 - Rodney Kongolo (Herenveen) £200,000 - Bobby Duncan (Liverpool) TOTAL = £239.5m Advertisement

Fundamentally, it's the club's investment in the first team - more than half a billion pounds under Guardiola alone - that for academy youngsters has all but shut the door to the first team.

Matondo said on moving to Gelsenchirchen: 'In footballing terms I wasn't a regular around the first team.

'I trained with the first team and it was a good experience training with Pep and the other players. They are top players.

'It is not City's fault, they have a wonderful team with wonderful players. But if you want to break in at City it is not going to be easy.'

Matondo's quotes are telling; while the opportunity to learn from the best is phenomenal, the chance to play alongside them remains minimal.

The need for trophies and establishing a position at football's top table has meant that promoting youth has had to take a back seat, as there is simply no room for risk - despite enormous investment in the academy.

Kieran Trippier has become Tottenham and England's right back after ditching City

Trippier in action for City in the FA Youth Cup semi-final against Sunderland in 2008

Denis Suarez bagged a transfer to Barcelona after developing as a youngster with City

The Spanish midfielder has since returned to the Premier League on loan at Arsenal

Whether this poses a competitive issue for City in the short term is questionable. They have just won an unprecedented treble.

Their first team is revered as potentially the best side in European football, while their academy investment hasn't exactly been misplaced either.

The club have profited too. In fact, despite the increased present-day market values of those they have sold, City's youth set-up remains the most profitable out of any top six side.

During the past five seasons, City have sold players who have made less than 15 senior appearances for the club for a total of £125.8m – and it will surely rise further with add-ons. This season alone, Angus Gunn departed for Southampton for £13.5m, Jason Denayer went to Lyon for £9.9m while Pablo Maffeo raked in £8.1m when he joined Stuttgart. That's before you add Matondo's £11m move to Schalke and Diaz's £22m switch to Real Madrid.

Not every player has decided to cut their losses either; Phil Foden, who recently signed a contract extension with the club to stay until 2024, has seen his first-team involvement improve year-on-year.

His goal against Schalke in the last-16 of the Champions League illustrates that an academy product can and does get opportunities in big games for the champions.

But making money does not address another more emotive accusation that by not bringing through or retaining their own talent, City are failing to cultivate the club's identity.

Sheikh Mansour himself referred to the importance of nurturing ties with the local community when outlining his vision for the club when he took over back in 2008.

'The cornerstone of the future was a vision for youth development and sustainability; a vision to educate talented young footballers on and off the pitch and to do so in a facility supported by the best coaches and coaching programmes,' reads his statement on the club's website.

'The vision was underpinned by an unwavering commitment to the regeneration of the local area in both economic and environmental terms.'

Kelechi Iheanacho has played more in City's first team than any recent academy graduate

Despite his early success, Iheanacho has been sold to Leicester amid fierce competition

In terms of investment and infrastructure, there is little doubt that Sheikh Mansour has lived up to his promise. City's academy have 17 pitches, two full-time coaches per age group from age 15 upwards and last season their Under 18s were national champions. Their Under 18s lifted the Premier League Cup.

But it is impossible to say the academy is currently sustaining the first team. Back in 2017, former club captain Paul Power voiced similar concerns about the importance of identity, and its absence at City. He said that the 'Manc had gone out of Manchester'.

'We need more Manchester,' he said. 'I don't care whether you are a supporter of Scunthorpe United or Manchester City, you want to see local players in your team.'

Foden, who is still only 18, is the club's only real answer to the accusation that they don't have 'one of their own'.

But the youngster is certainly not a regular, not yet anyway; he made 13 Premier League appearances last term, but 10 of those were off the bench.

Other clubs, meanwhile, do boast homegrown talent in their starting line-ups: Tottenham have Harry Kane and Harry Winks, Manchester United have Marcus Rashford, Jesse Lingard and others while Liverpool have Trent Alexander-Arnold. Even Chelsea, derided for neglecting their prolific youth set-up, still have Ruben Loftus-Cheek and now Callum Hudson-Odoi hovering around the first team.

This could and likely will change longer term. As City almost inevitably secure the titles they desire, the ridiculous spending on the first team will likely be reined back in.

With a transfer ban on the horizon and potentially harsher punishment from UEFA for allegedly manipulating Financial Fair Play rules, they could become more reliant on their academy than ever before.

However, the departures of Diaz, Matondo and Sancho suggest that it might not be straightforward to change the trend from youngsters seeking immediate success through the exit door.