Interim boss Frank Lampard remains winless since his return, and incoming manager Mauricio Pochettino will likely be aware of the huge job he faces at the Blues.
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Brentford took the lead in the 37th minute through an own goal from Chelsea captain Cesar Azpilicueta.
Blues fans booed off their side at half-time, with drastic improvement needed in the second half.
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However, they failed to show it, with Bryan Mbeumo coming off the bench and scoring the Bees' second of the night to secure the win.
Chelsea are now on 13 league defeats for the season so far, and remain 11th in the table.
The match was Lampard's 23rd Premier League fixture of the campaign too, with 14 of those being losses.
He has also won just one of his last 19 as a manager, with the Chelsea legend struggling to find a positive result as boss.
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Lampard is set to remain as interim manager until the end of the season but fans are beginning to grow impatient, especially after his bizarre starting XI for the visit of Brentford.
Pochettino is looking likely to be the next permanent appointment at Stamford Bridge, one who supporters will be praying can turn their fortunes around.
Some fans want him in now, with one Twitter user saying: "Get Pochettino in NOW, not later. We're suffering badly, this isn't even funny anymore, it's straight inhumane torture. We can't take this anymore, it's getting ridiculous."
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Another added: "Announce Pochettino now before he changes his mind @ChelseaFC."
A third simply said: "Bring Pochettino now I cannot do this."
talkSPORT understands that the former Tottenham boss has reached a verbal agreement with Chelsea to become their new manager.
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He was last at French giants Paris-Saint Germain where he won Ligue 1, the Coupe de France and Trophee des Champions.
Pochettino was also impressive during his spell at Spurs, guiding them into Premier League title races and a Champions League final.
However, his stint at Chelsea could very prove to be the toughest of his career so far.
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The Blues have scored just 30 goals in their 32 league games this season, the fifth lowest tally in the top flight.
A number of stars are set to be sold in the summer in order for the west London club to comply with Financial Fair Play.
Such departures are likely to give Pochettino a chance to bring his own signings through the door.
The Argentine believes he can make Chelsea Premier League title contenders once again, but it could be a while until they reach such heights.