#3 Andre Gomes
An impressive couple of seasons at Valencia followed by his eye-catching performances with Portugal at Euro 2016 convinced Barcelona to splash €35 million for Andre Gomes.
It was supposed to be a huge stepping stone in his fledgling career, the move even drawing plaudits from Cristiano Ronaldo who was then with Barcelona's Clasico rivals Real Madrid. However, after a positive start to life by contributing two goals in the Spanish Supercup, Gomes' form spectacularly nosedived.
The Portuguese midfielder struggled to adapt to Barcelona's style of play, looking woefully out of depth and failing to establish himself as a regular starter.
He was voted as one of the worst signings of the 2016-17 season by Marca readers. An injury-riddled second year made matters worse, prompting a loan move to Everton where he's now attempting to revive his career.
#2 Ousmane Dembele
Ousmane Dembele isn't yet a lost cause, but there's no denying that his career has significantly dipped since swapping Borussia Dortmund for Barcelona.
Plagued with recurring injuries, the Frenchman, one of the most highly-rated youngsters who had eye-catching performances with Rennes and the Schwarz-Gelben, has failed to reach his full potential at Barcelona after being sidelined for lengthy periods.
He has missed a staggering 80 games since arriving in Catalonia three years ago. Due to a serious hamstring tear, Dembele has featured only ten times for the club since the start of the 2019-20 season.
Make no mistake, Dembele has impressed in bits and parts, like with his sublime goals against Chelsea and Tottenham Hotspur in the Champions League. But a woefully poor health record so far has kept the star from reaching lofty heights.
#1 Arda Turan
Arda Turan was touted as the new Xavi Hernandez after arriving at Barcelona in 2016. He was tipped to fill in the shoes of the club legend who departed for Qatar the year before.
The Turkish star, who was signed for €34 million from domestic rivals Atletico Madrid, had established himself as one of the most complete and formidable attacking midfielders under Diego Simeone but couldn't live up to his lofty reputation at Barcelona.
Having waited for six months to make his debut owing to Barcelona's transfer embargo, Turan failed to nail down a starting spot under Luis Enrique and made just 14 starts during his first-full season in 2016-17.
The next campaign saw Turan get completely sidelined with back problems, which proved to be the last straw for him as the player returned to Turkey for a loan spell with Istanbul Basaksehi before joining his boyhood club Galatasaray in August this year.