#3 Danny Drinkwater

When Leicester City won the Premier League title in the 2015-16 season, everyone expected to see one of those big fish eat small fish situations.
Other than the obvious stars of the team, Jamie Vardy and Riyad Mahrez, the Foxes were buoyed by the excellent midfield partnership between N'Golo Kante and Danny Drinkwater.
So when Chelsea decided to partner Kante with Drinkwater at Stamford Bridge, they must have believed that it would work like a charm. However, it didn't go according to plan and Drinkwater ended up being iced out under Maurizio Sarri after making just 23 appearances for the Blues across all competitions.
He was bought for a sum in the ballpark of £35 million and is currently on loan at Super Lig club Kasimpasa.
#2 Alvaro Morata

Chelsea had to replace Diego Costa in the summer of 2017 and were initially linked with Romelu Lukaku. However, Lukaku ended up signing for Manchester United and Chelsea decided to bring in Alvaro Morata from Real Madrid and they paid €66 million for him.
Morata had enjoyed a fruitful loan spell at Juventus. After returning to Real Madrid, he was their second-choice striker but had managed to score more than 20 goals in the league. He came with a lot of expectations.
Morata faded after impressing initially and before long, he became a non-entity at the club. Morata scored a total of 24 goals from thrice as many outings for Chelsea and was sent on loan to Atletico Madrid with an obligation to buy. The 28-year-old is currently on loan at Juventus from Atletico Madrid and has been doing well so far.
But he will go down in Chelsea's history as a big-money flop and there is no way about it.
#1 Kepa Arrizabalaga

When Thibaut Courtois finally got his wish and secured a move to Real Madrid, Chelsea were tasked with finding a world-class goalkeeper who could replicate the Belgian's heroics between the sticks. They paid the big bucks but ended up with a faulty product.
Where do we start with Kepa? He is a nervy keeper who is extremely prone to errors and he doesn't have a great attitude either. Once tipped to displace David de Gea as Spain's no.1, Kepa Arrizabalaga is now Chelsea's biggest regret in their transfer history.
He was signed for £71.6 million and is currently third-choice at Chelsea under Edouard Mendy and Willy Caballero. Kepa has started just three games in the Premier League this season and has conceded six goals. That kind of sums it up, doesn't it?