Whether it be in terms of whether they didn’t play as well as you expected them to be, or if they were injured/unfit all the time during their career at your club or perhaps got on bad terms quickly into their career at your club (e.g. Di Maria at Man Utd).
As a Liverpool fan, I can think of names like Aquilani, Robbie Keane, Morientes, Andy Carroll, Kewell, Litmanen, Nuri Sahin etc.
But the one that has to take the cake is Naby Keita. I was very excited when it was announced he would be joining us. He was like the 2nd best midfielder in the Bundesliga that season for Leipzig in the data and for a couple of seasons had shown a lot of great technical ability. He joins us and the rest is history. It’s not to say he didn’t have good moments with us when he had a run of games in the first team. But that was presicely the issue, getting a run of games. It was a constant cycle of spending over half his time injured and when returning, not always having his best games due to slowly returning to fitness and when he did start showing his sparkle he’d go off injured again for a while. I am not just gutted for us but gutted for him too in how it could’ve and should’ve turned out.
Claudio Bravo would have to be our last signing to disappoint tbh, which says a lot about how well we do with new signings given he came 7 years ago 😂
An argument could be made for Kalvin Phillips but the man still has time to cook and really doesn’t look that out of place when he does play.
Ben Mendy also let us down but when he was playing he was electric so happy to give him a pass, plus you could also argue that with all the charges overturned it was City that let him down, not the other way around.
Before that the only signings I would consider total flops would be Wilfred Bony and Eliaquim Mangala