Lionel Messi is a phenomenon. 

He's been at the top of his game for over a decade now and hasn't shown any signs of slowing down. 

Only Cristiano Ronaldo has been able to constantly match him every season and both men can claim to be the greatest of all time.

Some argue that the Portuguese is superior due to the fact he's found success in three different leagues, with three different teams. 

Others argue that Messi's decision to spend his entire career at one club puts him on another level - because there's not much loyalty left in the game these days. 

In fact, the Argentine has never shown any intention of leaving Barcelona, despite the fact it's not always been plain sailing. 

Interestingly, it seems that should Messi want to walk away from Camp Nou, all he has to do is ask. 

According to El Pais, although his contract runs until 2021, the forward has the power to terminate it every summer, should he choose to do so. 

Per AS, the decision is placed solely on his wishes and his feelings at the end of the season, now he's reached 32 years of age. 

Considering he's still the best player in the world, it seems odd that Barca give him that option. But Messi doesn't want to be a 'slave' to renewals, and his club respect that. 

"We accept that he can stop whenever he likes, at the end of every season, and that's what both parties have agreed," a Barca source told El Pais. 

Interestingly, Messi's teammate Gerard Pique is also aware of the special clause, but he's not worried about the little magician leaving either. 

"I already knew Messi is able to leave for free at the end of each season," Pique told Spanish publication Cadena Ser, per the Independent

"We all know the commitment Leo has to Barca and it doesn’t worry me at all. He’s earned the right to be able to choose what he does with his future after everything he’s given the club." 

Messi is also not the first Barca player to be given a deal with this kind of clause. 

Legends Andres Iniesta, Carles Puyol and Xavi all had a similar agreement and Barca's decision to trust their loyalty never backfired.