Bobbie Jackson, BBC Sport
David Moyes had questions over the legitimacy of Brentford's winning goal, suggested there may have been an offside in the build-up at Gtech Community Stadium, but the Scot also had big questions for the state of his defence as they shipped three goals.
West Ham have conceded 20 times in the top-flight this season, with only Sheffield United, Luton and Bournemouth conceding more.
The defeat means they have only picked up one point from a losing position this campaign and it is just one win from their last seven in the top-flight.
After a strong start to 2023-24, which saw West Ham picked up 10 points from the first 12 on offer, they have only collected four points from the last 21 available.
It was not all doom and gloom for the Hammers, though, with Jarrod Bowen once again catching the eye.
Bowen grabbed his seventh league goal of the term, surpassing his tally of six from 2022-23, and he made history by becoming the first player in Premier League history to score in his side's first six away games of a season.
Mohammed Kudus also impressed when scoring an acrobatic bicycle kick in the first half - registering for the second successive game.
It is back to the Europa League next time out for the Hammers with Olympiakos travelling to the London Stadium on Thursday.