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At a comparatively paltry £20 million, Alberto Aquilani doesn't seem to match up to the other names on our list, particularly as he didn't so much fail as barely get a chance to prove himself.
His time at Anfield was beset by a constant string of injuries, and he made just nine league starts in three years at the club.
However, it's when considering the man that the Italian was brought in to replace that the folly of his transfer becomes obvious. Xabi Alonso, one of Rafael Benitez's first signings upon becoming Liverpool manager, had established himself as arguably the best ball-playing defensive midfielder in the world while at the club.
This apparently wasn't enough for Benitez, who tried to replace him first with Gareth Barry before finally shipping Alonso to Real Madrid for around £30 million.
Ostensibly, replacing Alonso and netting £10 million didn't appear to be bad business for Liverpool fans, who had much faith in Benitez's judgement. Sadly, Aquilani never looked like a player worth two-thirds of Alonso when fit—which was rare.
The loss of a quality player in the quarterback role was a devastating blow to both Benitez's system—which relied on the position heavily—and the club's squad, which only last season looked to be finally moving on from the loss of the Spaniard.
Aquilani was quietly moved on to Fiorentina in 2012 for free, having spent the previous two seasons on loan in Italy.