When Barcelona confirmed they had received a request from Lionel Messi's lawyers informing them he wanted to terminate one of soccer's longest-standing relationships, the owners of Europe's biggest clubs would have raised a collective eyebrow.

It was akin to the Mona Lisa suddenly becoming available on the art market, such is Messi's status in the game despite the fact that he is 33 and the magic might soon begin to fade.

Already the usual suspects are being lined up as Messi's next club with, not surprisingly, a reunion with his former manager Pep Guardiola at Manchester City the most likely scenario according to the bookmakers.

There is talk of Messi joining forces with Cristiano Ronaldo, his long-term rival as the world's greatest player, at Juventus or linking-up again with Neymar at Paris St Germain as they bid to end their Champions League jinx.

Inter Milan's Chinese owners would also see Messi as the player to turn them back into a European force.

Rolling TV sports channels and social media were buzzing with Messi's Barca bombshell on Wednesday.

Yet despite the inevitable excitement, it is by no means certain Messi will have multiple options if the split with the Catalan giants he joined as a teenager in 2001 is irreparable.

Messi insists a clause in his contract allows him to leave for free a scenario that would attract a frenzy of suitors.

Barcelona, however, say that clause has expired and a rival club must pay his release clause of 700 million euros ($826 million) if he is to leave without the club's consent.

Should Barcelona stick to their guns it would knock most potential buyers out of the ball park, especially with Messi's one million euros per week salary demand.

The marketing men will point to the avalanche of shirt sales and Messi merchandising that the six-time Ballon d'Or winner would guarantee, not to mention his disciples around the globe swelling the club's fanbase.

Finances aside, though, there is an even bigger question mark hanging over Messi. Is he a fading force?

It sounds churlish to suggest that of a player who remains the heartbeat of one of Europe's biggest clubs for whom he has helped win over 30 trophies, but none last season.

Yet his 31 goals in all competitions last season, impressive by ordinary standards, was not exceptional.

After all, this is a player who holds the La Liga scoring record of 444. He once scored 79 club goals in a calendar year, and is the only player to score more than 40 goals for his club in 10 consecutive seasons.

Messi's disenchantment with the club's hierarchy, notably club president Josep Maria Bartomeu, could have been a factor in the transfer request but even a footballing genius cannot defy the passing years.

On the other hand a fresh challenge might spark a golden final chapter to his glittering career. The question is where?

Messi has made no secret of his admiration for the Premier League and Manchester City would seem the most logical fit.

Guardiola would surely relish a reunion with Messi as he rebuilds a side eclipsed by Liverpool last season.

After their brush with UEFA's Financial Fair Play rules, even Abu Dhabi-owned City might shy away from a 700 million price tag, especially with other areas of the pitch in serious need of strengthening.

Manchester United's owners, the Glazer family, might see signing Messi as a way of winning over sceptical fans, while Chelsea's benefactor Roman Abramovich has re-opened his chequebook with a vengeance and will, like the rest of the soccer world, be closely monitoring events.