Chelsea have been one of the most active clubs in the transfer market ever since Roman Abramovich took over the team in 2003. The Blues have become a powerhouse and are one of the most feared teams in the Premier League, thanks to a number of world-class talent at their disposal.The likes of Didier Drogba, Frank Lampard, Petr Cech and Eden Hazard have plied their trade at Chelsea to become superstars during their time at the club.Not all players enjoyed similar success after joining ChelseaWhile the aforementioned players were able to replicate their success at Stamford Bridge, a few were not so lucky. These players arrived at the club with lofty reputations only to see themselves fail on the pitch for the Blues. They did not enjoy their time at the club and would surely rue putting pen-to-paper on the move to Stamford Bridge.Here we take a look at five such players who regret joining Chelsea:#5 DecoChelsea v Girondins de Bordeaux - UEFA Champions LeagueDeco arrived at Chelsea with a big reputation in 2008 from FC Barcelona. The little Portuguese maestro cost Chelsea just £8 million, which was considered a bargain for a player of his quality. Deco won the Champions League with Porto in 2004 and with Barcelona in 2006. He even finished as a runner-up in the 2004 Ballon d'Or race, behind Andriy Shevchenko.Deco started his Chelsea career with a bang, scoring a screamer on his debut and winning the Premier League Player of the Month award at the first try.Happy birthday to former Chelsea player Deco. pic.twitter.com/QYDzCjWACe— Frank Khalid (@FrankKhalidUK) August 27, 2020But the Portuguese was unable to maintain his form and reach the same heights that he achieved at Porto and Barcelona. Injuries have also plagued him throughout his time in England. Deco left the club in 2010 after playing just 42 games and scoring five goals. He joined Fluminese on a free transfer.Considering Deco's legendary status at Porto and Barcelona, he would have definitely regretted joining Chelsea after his poor spell at the club.#4 Tiemoue BakayokoChelsea v AFC Bournemouth - Carabao Cup Quarter-FinalPart of the famous Monaco team that overthrew Paris Saint-Germain to become Ligue 1 champions, Tiemoue Bakayoko arrived at Chelsea with a lofty reputation. Chelsea splashed out £40 million for the midfielder in the hope that he would form a strong partnership with N'Golo Kante in the middle of the park.However, after a series of poor performances in his debut season, he was sent on to loan to AC Milan for the 2018-19 campaign. Chelsea then switched managers from Antonio Conte to Maurizio Sarri and Bakayoko was simply not going to be a part of the latter's plans.The Frenchman was impressive at Milan but the Rossoneri decided against making the switch permanent due to Chelsea's asking price. He spent the next two seasons on loan at his former club Monaco and with Serie A giants Napoli.Bakayoko has re-joined AC Milan this summer on a two-year loan deal with an option to buy. He will definitely be hoping to put in impressive performances so that the Rossoneri can activate his clause and end his Chelsea nightmare.DONE DEAL: Tiemoue Bakayoko joins Milan on loan from Chelsea for the second time 🤝 pic.twitter.com/3pgljQfNpR— Goal News (@GoalNews) August 30, 2021