But how does the Argentine's lucrative deal compare to the eye-watering remuneration on offer elsewhere?
Grab your abacus and join us as we examine some of sport's biggest paydays…
NBA - STEPH CURRY
Two-time MVP Curry has agreed a new deal with Golden State Warriors, the point guard inking the NBA's first contract to break the $200 million barrier.
A major improvement on the rookie extension an injury-prone Curry signed in 2012, it is worth $201,158,790 across five years according to Sportrac, or £648,877 gross per week.
MLB - CLAYTON KERSHAW
Los Angeles Dodgers starting pitcher Clayton Kershaw signed on the dotted line of a seven-year, $215m contract in 2014. That's £495,494 per week gross for MLB's best-paid player.
NFL - DEREK CARR
Quarterback Derek Carr's $125m deal over five years with Oakland Raiders works out at £403,308 per week gross. Less than Kershaw, a lot less than Curry and nowhere near Messi.
F1 - FERNANDO ALONSO
Surprisingly, four-time world champion Lewis Hamilton of Mercedes is not Formula One's best paid driver as negotiations over a new deal with Mercedes continue. That accolade goes to Fernando Alonso, who is paid $40m per year, or £645,294 gross per week, to drive an uncompetitive McLaren.
CRICKET - VIRAT KOHLI
India cricket captain Virat Kohli is believed to have earned $2.5m from Royal Challengers Bangalore in the 2017 Indian Premier League.
While that's considerably less than most of the athletes on this list, Kohli only made 10 appearances for RCB this season, which works out a handy £193,682 per match.
BOXING - FLOYD MAYWEATHER JR
Living up to his nickname, 'Money' is understood to have banked approximately £230m for his much-hyped victory over Manny Pacquiao in 2015.
That's £4,951,839 per minute or, if you prefer, £82,530 per second during the course of the bout. There was another guaranteed $100m banked for his 10-round blowout against UFC star Conor McGregor before pay-per-view receipts were counted.
Even with the might of Barcelona and Argentina behind him, there's no way Messi can match that hyper-intensive earning power over such a short spell of action.
“MR. UNDEFEATED”— Floyd Mayweather (@FloydMayweather) October 5, 2017
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FOOTBALL - RONALDO, TEVEZ, LAVEZZI
Cristiano Ronaldo is believed to receive £424,000 after tax from Real Madrid, while Carlos Tevez of Shanghai Shenhua is said to get £634,000 per week gross.