#3: Samuel Eto'o (Moved from Barcelona to Inter Milan in 2009)
In a career that took him to 13 different clubs across six different countries, Samuel Eto'o undoubtedly had his most proflic spell with Barcelona.
The Cameroonian striker arrived at Camp Nou after first making his name at Mallorca, but it was at the Catalan capital where Eto'o rose to even greater heights.
Regarded as one of the best African players of all time, Eto'o was renowned for his stamina, work-rate, composure in front of goal and aerial prowess. Although deployed mostly as a centre-forward, Eto'o could also operate in other areas in the attacking third with consummate ease.
All of his attributes came to the fore during his debut season at Barcelona as Eto'o scored 25 goals in his club's victorious La Liga campaign. A season later, he went one better to win the coveted Pichichi award while also scoring the equaliser against Arsenal in the 2006 Champions League final.
After two relatively lean seasons, Eto'o was back at his blistering best, combining brilliantly with the likes of Messi and Iniesta as Barcelona won their first continental treble in 2008-09. However, at the end of the season, the Cameroonian international made a surprise move to Inter Milan in a swap deal, with a certain Zlatan Ibrahimovic moving in the opposite direction.
"Samuel is a wonderful player and he did so well last year. Samuel has his character, his personality makes him what he is. There is not a single major reason for this decision. It is a matter of feeling and sensations. It's just that after winning the so much, we must change the squad, that's all, there are no other reasons."
Not for the first time, Barcelona's loss turned out to be Inter Milan's gain. In his first season with the Nerazzurri, Eto'o joined a select group of four players to win back-to-back Champions League titles and was probably the first player to win back-to-back continental trebles with two different clubs.
#2: Thiago Alcantara (Moved from Barcelona to Bayern Munich)
Thiago Alcantara is a creative playmaker with excellent dribbling and ball-control skills, which is ideal for his deployment as a central midfielder. However, he is also versatile enough to operate with elan in a more advanced midfield role.
The La Masia graduate started his career at Barcelona in the summer of 2008 but made only two appearances in his first two seasons with the Blaugrana. Things improved slightly, especially in 2011-12 and 2012-13, as the Brazil-born star made over 80 appearances in all competitions and scored seven goals.
However, with an eye on making Spain's 2014 FIFA World Cup squad, Alcantara, who didn't start enough games at Barcelona, decided to shift base to Bavaria where he became former Blaugrana boss Pep Guardiola's first major signing at Bayern Munich.
The son of 1994 FIFA World Cup winner Mazinho of Brazil, Thiago Alcantara marked his Bayern Munich debut with a goal in the 2013 Club World Cup final and didn't look back. Despite the departure of Guardiola, Alcantara continued to blossom under new manager Carlo Ancelotti, producing a staggering pass-completion rate of 90% in the 2016-17 Bundesliga.
After seven seasons in which he won 16 trophies, which included the continental treble last season, Alcantara decided to leave Bayern but not after leaving an indelible imprint on the club, something he could have also done at Barcelona if only they didn't have a stacked midfield.
#1: Neymar (Moved from Barcelona to Paris St. Germain in 2017)
Along with Lionel Messi and Luis Suarez, Neymar formed one of the most fearsome attacking triumvirates in world football, which was affectionately nicknamed MSN.
Predominantly a left-sided forward, Neymar can also operate as a central striker, winger or even as an attacking midfielder because of his electric pace, dribbling skills and playmaking prowess.
The Brazilian scored 108 goals in 186 appearances during four glorious seasons as Barcelona won a plethora of titles in domestic competitions and abroad, which included the club's second continental treble in 2014-15.
However, Neymar largely operated under the shadow of Barcelona's talisman Lionel Messi and felt that he may not realise his ambition of winning the coveted Ballon d'Or if he stayed on at Catalonia.
Paris St. Germain were alerted, and the French club, backed by oil-rich owners, splashed out €222 million in 2017 to make Neymar the most expensive player in world football.
Barcelona have never really recovered from the loss of Neymar. They have since tried a bevvy of expensive acquisitions to fill the void left by the Brazilian but with little to no success. Neymar was particularly missed last season as the Blaugrana endured their first trophyless season in 12 years with a 2-8 humbling against eventual champions Bayern Munich.