Lionel Messi's timeline of events at Barcelona that have caused him to want to leave

The unthinkable could happen. Lionel Messi could be playing for a club not named Barcelona next season.

The Argentine talisman's future at the Spanish giants appears to be in grave doubt after he told them by fax that he wants to leave on Tuesday.

The culmination of this message follows a year of grumblings between the two parties. So where did it all go wrong? Sportsmail looks at how Messi's relationship with Barcelona has worsened at the Nou Camp.

No Neymar (summer 2019)

Let's start with last summer. Barcelona ended the 2018-19 season as winners of LaLiga but had room for improvement after squandering a 3-0 first leg lead in the Champions League semi-finals to Liverpool (they lost the second leg 4-0), while they were beaten 2-1 by Valencia in the Copa del Rey final. Messi knew the club had to strengthen and implored the board to re-sign former Barca team-mate Neymar.

Neymar and Messi had been team-mates for four years before the former sought pastures new and joined Paris Saint-Germain in a world-record £198million transfer in August 2017. However, the Brazilian appeared to have grown tired of life in Paris and yearned for a return to Barcelona. As a result, Messi called for those at the top to bring his friend back to Spain.

Barcelona were put off by PSG's asking price of £269m (a £71m rise in the fee that saw the clubs do business the other way around) and their botched attempt at negotiations didn't impress Messi. There were a couple of public flights by technical secretary Eric Abidal (more on him later) which were seen more as a token gesture to Messi that they were trying.

After failing to sign Neymar, the club plumped for Antoine Griezmann from Atletico Madrid instead but he hasn't gelled with Messi on the pitch.

Ernesto's exit (January 2020)

Picture the scene. You've helped the club to two successive LaLiga titles and you lead the current campaign's title race on goal difference. Yet you're relieved of your duties. Well, that's the fate that befell Barca boss Ernesto Valverde on January 13.

Despite some poor results - most notably the Champions League capitulation at Liverpool - and criticism over his style of play, Valverde was still delivering results. His dismissal irked Messi who was close with the Spaniard and would have kept him on.

Writing on Instagram, the Argentine tipped Valverde for future success, calling him a 'magnificent person'.

'Thank you for everything,' he said in the social media post. 'I'm sure you'll do great wherever you go because besides being a great professional you are a magnificent person.

'Good luck and a big hug.'

Instead the club appointed Quique Setien as Valverde's replacement and he signed a two-and-a-half-year deal. Fast forward from January to August and Setien is no longer manager of Barcelona after he too was sacked following an abject short spell.

Setien and Messi didn't appear to have a great working relationship - with the latter completely ignoring his backroom staff during their 2-2 draw at Celta Vigo in June.

Anger at Abidal (February 2020)

It would have been hard to fathom that Abidal and Messi would ever have a public fallout, and to the extent that which they did, when the latter became the club's technical secretary at the start of last season.

The pair were team-mates during the golden era at the Nou Camp - winning four LaLiga titles and two Champions League over the course of six years.

However, the former France left back's decision to sack Valverde and his subsequent comments about the squad being behind the dismissal saw his relationship break down with Messi.

Many players 'weren't satisfied or working hard and there was also an internal communication problem,' Abidal told Diario Sport.

'The relationship between the coach and the dressing room has always been good but there are things as an ex-player that I could smell. I told the club what I thought and we reached a decision [on sacking Valverde].'

Abidal's comments irked Messi who responded on Instagram to defend himself and his team-mates: 'When you talk about players, you have to give names because if not, it gives air to things which are not true,' he wrote.

And speaking about his part in the public spat in February, Abidal acknowledged he went about it the wrong way.

'If I know something and if I have learned anything it is that internal issues are arranged in house and not in the media,' he told reporters at the introductory press conference for signing Martin Braithwaite.

Abidal's comments followed Messi's take on the situation in an interview in Mundo Deportivo where he said he responded to his former team-mate's criticism because he 'felt attacked'.

Messi, who was close to Valverde, said: 'I don't know what happened to make him say that but I responded because I felt attacked. I felt he was attacking the players.

'Too much is said about the dressing room, that we force coaching changes or bring in players, and especially about me - like I have a lot of power and make the decisions. The same happened to me in the Argentine national team.

'It bothered me coming from someone from the club... to put the players in the middle of the dismissal of the coach seemed crazy. (Abidal) is the one who makes the decisions and has to take charge.'

Displeasure at Bartomeu (the whole season)

Take your pick with this one.

In essence, Messi wants change at the very top and that means a new club president. Josep Maria Bartomeu has one year left of his presidency but has no desire to quit early - despite growing discontent.

The failure to sign Neymar and the sacking of Valverde are two major factors. The fact that they were thumped 8-2 by eventual winners Bayern Munich in the Champions League quarter-final is another reason.

The board are looking to overhaul the playing squad but Messi wants the board overhauled.

He has always had an excellent relationship with former president Joan Laporta and he may well stand in the next election. Another candidate Victor Font would also appear better equipped than Bartomeu.

Following Tuesday's shock news, Laporta blamed Bartomeu for the stance stance taken by Messi.

'Bartomeu and his board should quit immediately,' he tweeted. 'They have undermined Messi to save them from the sporting and financial mess they have created. If they quit there might be some hope that Messi stays at Barca.'

The discontent has spilled over to the fans who were outside the Nou Camp on Tuesday night shouting 'Bartomeu resign!'

Letting go of Luis (August 2020)

On Monday, reports in Spain emerged that Barcelona have informed star striker Luis Suarez that his six-year spell at the club is over. As mentioned in the previous section the board are looking to overhaul the playing squad - a sentiment echoed by newly-appointed manager Ronald Koeman who sees Suarez as one whose time is up.

RAC1 reported that Koeman told the 33-year-old that he is not in his plans at all, following a phone call on Monday. Suarez is currently on holiday but was informed of the decision in a 'brief conversation' between the two.

His contract, worth £290,000 per week in wages, doesn't expires until June 30, 2021 and there is an option on that to extend it by another year. However, RAC1 say the next step is for Suarez's lawyers to negotiate the termination of his contract.

This has apparently annoyed Messi who is extremely close with the Uruguayan - with the duo often going on holiday together with their families as has already been the case this summer. On top of that too, Messi still believes Suarez to be integral to Barca and sees the striker as only one of a few within the squad who is on the same wavelength as him.

Furthermore, Koeman's plans for Barca next season have reportedly ruffled Messi's feathers after the Dutchman told him he won't be treated differently from his team-mates.

Argentine news outlet Diario Ole claims at a meeting Koeman told Messi: 'Your privileges in the squad are over, you have to do everything for the team. I'm going to be inflexible, you have to think about the team.'

The frank exchange reportedly convinced Messi that now is the time for him to leave the club.