This is one of a myriad of reasons that has led to uncertainty over the future of manager Antonio Conte, whose presence at the club is influential in the steps they take going forward.
The Italian has already shown that he is not afraid to make big changes, with last season's top scorer Diego Costa notably shipped out to Atletico Madrid.
Regardless of how the season ends for the Blues, alterations are clearly required and Goal takes a look at the players who should stay and those who should be cut loose at Stamford Bridge.
Players who should go
David Luiz – Luiz is a Chelsea legend and his departure from the club wouldn't be greeted with glee by either fans or the ownership of the club.
However, his relationship with Conte is tense. The emergence of Andreas Christensen has allowed his manager to drop his other ball-playing defender, and the Brazilian has, as such, grown unsettled. The relationship with his manager might have led to poor performances, but Luiz has looked below his usual level, particularly in the matches against Roma and Watford.
He is too good to rot on the bench, but his lack of appearances can also be attributed to a knee injury that he sustained from a flying tackle from Sergio Aguero in December 2016.
Michy Batshuayi – The Belgian international has eight goals in his first 11 games for Borussia Dortmund and has quickly impressed his new club, who want to sign him on a permanent deal.
Conte was a fan of Batshuayi's finishing but didn't think he did enough in his link-up play to justify his selection. He even opted to play Eden Hazard as a false nine ahead of him when Alvaro Morata was injured or out of form.
Batshuayi is another player whose future may be tied to whoever ends up leading Chelsea next season.
Ruben Loftus-Cheek – Loftus-Cheek has produced some brilliant performances at Crystal Palace in his first loan move away from Chelsea since signing for the club as a young boy.
The spell has allowed him to make his England debut, but he has unfortunately since had a long period out injured.
The 22-year-old would command a high fee but his spell with Palace has shown that he needs to play regular football to take his game to the next level.
Other Chelsea loanees – A number of Chelsea loanees are reaching maturity and may leave the club for the right offer. Marco van Ginkel has been out on loan for a number of years and is the captain of PSV, despite not being a permanent member of the squad.
The Dutch side have pushed to sign him on a permanent deal, but couldn't agree on a fee with Chelsea. Newcastle United are expected to try and sign Kenedy again in the summer after seeing him immediately impress at the club during his temporary move.
Players who should stay
Eden Hazard – He is Chelsea's talisman and he can retire as the club's greatest ever player if he remains at Stamford Bridge for the rest of his career. It is a big ask, however, in light of this disappointing campaign.
Thibaut Courtois – Come June 30, 2018, Courtois will be in the final year of his Chelsea contract. He is interested in a move to Real Madrid and, if he leaves, it would be a blow to Chelsea. He hasn't made a firm decision on his future and Chelsea are hopeful that he will renew his deal after the season is over.
His poor performance against Barcelona shouldn't mask the fact that he is among the top 10 goalkeepers in the world and he would be expensive to replace.
Alvaro Morata – Morata has only scored once in 2018 and his dry spell has led to him being dropped from big games. Julen Lopetegui also left him out for the Spain national team, but he says Morata remains in contention for the World Cup.
It looks bad for the ex-Real Madrid and Juventus hitman right now, but he remains a big asset for Chelsea and he must use this season as a transitional one. Chelsea are not going to give up on him delivering as their record signing and he will still get his chance to take his game to the next level at Stamford Bridge.
Cesar Azpilicueta - Like Hazard, Azpilicueta can achieve legendary status at Chelsea and is already operating as vice-captain. He is playing more than Gary Cahill and has become one of the first names on the team sheet.
He is hugely popular with the fans and is on a long-term contract. It is unlikely that Chelsea would let him go lightly and Azpilicueta looks comfortable at the club, which has taken his game to the next level.
N'Golo Kante – Kante is arguably Chelsea's best player and he has already pledged his future to the club for next season, despite interest from Paris Saint-Germain. At £32 million, Kante looks a bargain, having won numerous Premier League Player of the Year awards last season. The 26-year-old will be valued by whoever ends up managing Chelsea.
Cesc Fabregas – Fabregas is playing more games than ever, with Tiemoue Bakayoko struggling for form and Danny Drinkwater and Ross Barkley often injured. The 30-year-old has already carved an incredible legacy in football and doesn't look like he is finished yet. He has adapted to survive under Conte, who prefers physical midfielders. Meanwhile, Fabregas enjoys living in London with his family and will not want to leave.
Andreas Christensen – Conte is a huge fan of Christensen and regards him as the present and future of Chelsea. He has been earmarked as a special talent for a number of years after impressing upon his arrival at the club at 16 years of age. Christensen should be targeting status as one of the world's best defenders and his contract renewal this season ensures that Chelsea's rivals won't find it easy to poach the Denmark international.
Antonio Rudiger – Rudiger has arguably been Chelsea's best signing, having arrived for £30 million in the summer from Roma. He has ousted club captain Gary Cahill for his regular spot in a battle that lasted a number of months. The highly regarded German's versatility should mean that he remains at the club for a long time.
Willian – Willian is in the form of his life, notching his best return at Chelsea of 13 goals in a single season. Also bringing assists, the Brazil international looks undroppable at the moment with his eye-catching displays.
The rest – Emerson Palmieri and Ross Barkley are expected to be given more time, having been signed after recently recovering from long-term injuries. Willy Caballero will likely be offered another contract as he impresses as back up to Courtois. Olivier Giroud has only an 18-month contract at the club, but will stay. Davide Zappacosta has been in and out of the Chelsea team, but should remain, especially if Conte does.
Playing for Chelsea future
Tiemoue Bakayoko – The £40 million signing from Monaco has, so far, been a disaster at Chelsea. His performances have been pivotal in a number of games and he has failed to fill the gap left by Nemanja Matic. He is still only 23-years-old and Chelsea will want to see him play out another season after struggling to adapt in his first year in the Premier League. However, Bakayoko faces a battle to show his manager, whether it is Conte or someone else, he is worth persevering with.
Danny Drinkwater – The England international has not had the season that he would expect at Chelsea and has struggled to get a run of games in the first team. His season has been hampered by injury, but he has still failed to convince Conte that he is the man who should play alongside Kante. The £35 million signing looks like an outsider for the World Cup, despite his country's lack of options in his position.
Pedro – Chelsea's policy around player contracts is to only offer one-year deals for their stars who are over 30. Pedro has reached 30-years-old and has only one more year left on his deal. He has struggled this year, having had three separate injuries, and his form hasn't fully recovered. Conte remains a fan of Pedro, but his lack of form may be enough to convince the club to cash in on him, should the right bid come along.
Gary Cahill – Cahill is the club's captain and an important figure, but his lack of appearances under Conte have seen him left out of the England squad ahead of the World Cup. The 32-year-old has been a regular for his country ever since joining Chelsea, but he has only made one start in the past month. The Chelsea captain's deal expires in 2019 and, as a player with legendary status at the club, he will likely be listened to if he wants to leave for more first-team football.