Chelsea have spent a huge amount of money on players and infrastructure since Russian oligarch Roman Abramovich took over the club in 2003. Part of the infrastructural development was to improve the academy. This decision has proven to be fruitful for Chelsea, with their youth set-up among the best in England, if not across Europe.Academy graduates saved Chelsea during transfer ban.When Chelsea were banned from signing any players in 2019, manager Frank Lampard quickly turned towards some of the young players groomed in the academy. This move saw Reece James, Mason Mount, Tammy Abraham, Fikayo Tomori and Billy Gilmour thrust into the first team, and they have thrived ever since.It should be noted that before Lampard, other Chelsea managers tended to use academy players as an afterthought, forcing many to leave the club. A number of outrageously talented youngsters have come through the Chelsea youth set-up in recent years, but few have gone on to become seasoned stars.Here is a list of five Chelsea youngsters who failed to live up to the hype they generated when they first broke through.#5 Michael MancienneChelsea FC v Club AmericaEnglish midfielder Michael Mancienne was touted as one for the future. As a youngster, he got his first Three Lions call-up even before he made his Premier League debut. Mancienne was capable of playing across the backline and also in defensive midfield, making him a valuable asset to the club.Mancienne joined Chelsea as a nine-year-old and made his debut in the 2008/09 season, playing in the league, Cup and Champions League. He was named the club's Young Player of the Year and rewarded with a new four-year contract but never played another game.Chad ⭐⭐@ChelseaChadderOn this day: 2009 - Michael Mancienne made his @ChelseaFC debut. #CFC #Chelsea10:30 AM · Feb 14, 2021634On this day: 2009 - Michael Mancienne made his @ChelseaFC debut. #CFC #Chelsea https://t.co/62DhABsRDfMancienne left Chelsea for Wolverhampton Wanderers before embarking on a journey around the world. Now 33, Mancienne plies his trade with Burton Albion in the lower rungs of English football.#4 Lucas PiazonChelsea v Malaysia XIWhen Chelsea brought in a teenage Lucas Piazon, word quickly spread that the club had secured the signing of the next Kaka. Blessed with a similar stature to the Brazilian Ballon d'Or winner, Piazon was supposed to be the next big thing at the club.Aged 18, he was named the club's Young Player of the Year in 2012 after impressing greatly for the youth sides in various competitions. Piazon made his sole Premier League appearance in late 2012, assisting a goal and winning a penalty which he missed in Chelsea's 8-0 drubbing of Aston Villa.It would turn out to be his last appearance for the club before he started a series of loan moves over the next eight years of his career.Ikemba Zaza🦁🐾@mazi_ikembaBrazilian born striker Lucas Piazon, joined @ChelseaFC from São Paulo in 2011 after stellar performance at U-17 in Mexico. After 10yrs at the bridge, d talented player who can play as a winger, now pitched tent with Braga FC, with only 3 appearance & 0 goals for the blues. #CFC2:45 PM · Aug 8, 202165Brazilian born striker Lucas Piazon, joined @ChelseaFC from São Paulo in 2011 after stellar performance at U-17 in Mexico. After 10yrs at the bridge, d talented player who can play as a winger, now pitched tent with Braga FC, with only 3 appearance & 0 goals for the blues. #CFC https://t.co/1jkmRh1O2TThe Brazilian secured a permanent deal with Portuguese outfit Braga in 2021 to end his ten-year association with Chelsea.