In 2015, Lionel Messi and Barcelona were on top of the world.

Led by Messi - alongside Neymar and Luis Suarez in a devastating 122-goal attack - the Blaugrana claimed their second treble with Champions League success, then making them the first European club to achieve such a feat.

The Club World Cup title followed for Luis Enrique's side, but such supremely high standards were not maintained.

Five years later, the 'MSN' front line has long since been broken up by Neymar's departure - and now Messi intends to follow his former colleague out of Camp Nou.

Barca did not win a single trophy in a 2019-20 campaign that ended in humiliation with the 8-2 defeat to Bayern Munich that prompted Quique Setien's sacking before Messi's shock transfer request.

Just where has it all gone wrong for one of the world's biggest clubs? We take a look.

JUNE 2015: Barca batter Bianconeri in Berlin

Suarez's 2014 move from Liverpool had been a roaring success for Barca even before they took to the field against Juventus in the Champions League final. Linking up with Messi and Neymar to great effect, an ambitious attacking approach made them arguably even better on the eye than Pep Guardiola's outstanding 2008-09 team.

Then Barca took Juve apart in Berlin with goals from Ivan Rakitic, another new signing, Suarez and Neymar and history was theirs. It appeared Messi and Co could do no wrong.

APRIL 2016: Wobble costs European crown

Barca's serene progress continued into the next season and, heading into April, they had lost just three times in all competitions, in the process becoming world champions for the third time - again a record at that stage.

But the Blaugrana then sensationally lost four of their first five matches in April. Three straight LaLiga defeats did not cost Luis Enrique's men the title, but the Champions League quarter-final second-leg reverse at the hands of Atletico Madrid ended their continental dominance amid a Messi goal drought.

APRIL 2017: Neymar's rescue act proves in vain

It was in the 2016-17 campaign that Luis Enrique's reign came to an end, with news of his impending departure confirmed in early March. Neymar did his utmost to send the coach in style, though, with a heroic performance against future employers Paris Saint-Germain, a dramatic late brace teeing up the remarkable 6-5 aggregate win in the Champions League.

That triumph kept Barca's latest treble bid on track, but it soon faltered. They lost 3-0 at Juve in April and were shut out in the return leg, while rivals Real Madrid marched towards the domestic championship, seeing Luis Enrique bow out in relatively underwhelming fashion.

AUGUST 2017: Selecao superstar stuns the world

Crucially, Luis Enrique was not the only man to depart Camp Nou at the end of the 2016-17 season. Neymar appeared to enjoy his role as the main man in the PSG tie, so the Brazil superstar traded Barcelona for Paris in a stunning €222million move.

The huge fee seemed to burn a hole in the Blaugrana's pocket as the first of several unsuccessful attempts to replace Neymar took them to Germany to buy Ousmane Dembele. Philippe Coutinho followed in January, with the duo struggling for form and/or fitness.

APRIL 2018: Roma remontada ruins campaign

Barca won back the LaLiga title under Ernesto Valverde in 2017-18, also claiming the Copa del Rey, yet their season still ended in disappointment in what would become an extremely concerning theme.

Valverde's outfit won 4-1 at home to Roma in the Champions League quarter-finals to all but seal their progress, only to incredibly go down 3-0 in Italy and crash out, extending Messi's wait for a fifth European triumph by another year.

MAY 2019: Reds inflict humiliating repeat

The next season felt far too familiar for Messi and Barca. In 2015, winning had felt second nature. By 2019, even the most extraordinary of collapses seemed very on-brand.

After failing to bring back Neymar and instead blowing a huge sum on Malcom, yet still easing to LaLiga glory, Barca remarkably again threw away a three-goal advantage in the Champions League. Liverpool overturned a 3-0 first-leg deficit in the semis with a 4-0 Anfield success as the Catalan side imploded once more.

FEBRUARY 2020: Abidal at war with Messi

Matters on the field were relatively steady this term prior to January's Supercopa de Espana defeat to Atletico Madrid, with Barca still in control of the league title race. But then Valverde was sacked and sporting director Eric Abidal made the mistake of blaming the squad for not working hard enough.

Messi responded with indignation and a hugely damaging feud was launched via a series of back-and-forth comments and briefings, appearing to publicly place significant strain on the club's relationship with their talisman for the first time.

AUGUST 2020: Bayern loss the breaking point

Relations were still a little rocky between Messi and the board through football's coronavirus-related shutdown, but for all Barca's troubles in recent years, their ability to rely on one of the greatest players in the history of the sport has so often been a saving grace. Messi dragged them past Napoli in the Champions League.

But even a Barcelona lifer like the great number 10 appears to have a breaking point. The 8-2 humbling at the hands of Bayern meant even the departures of Setien and Abidal could not convince Messi to stick around and influence a mammoth rebuild, with Suarez also set to depart.