Real Madrid have retained their place as the most valuable football team in the world for a third straight year, but Manchester United could soon topple them.

The reigning European champions' value has dropped 5% to $3.26billion, but their $746million revenue is the highest of any sports team in the world.

Rivals Barcelona are second in the 2015 list with a value of $3.16billion, followed by Manchester United at $3.10billion.

Unlike the Spanish giants, however, the value of Louis van Gaal's side has grown this year, with Forbes reporting a 10% increase.

No club are as adept at acquiring sponsorship as United, with US car giant Chevrolet's kit sponsorship deal worth a reported £53million per season.

Next term the coffers are to be boosted further after a mammoth £750million deal was struck with Adidas - a "global technical sponsorship and dual branded licensing deal" running for 10 years.

United believe it is the biggest kit deal in sport and may well help them surpass Barcelona and Real Madrid, especially given the recent £5.136billion Premier League television deal.

The Old Trafford giants are one of eight Premier League sides in the top 20, with Manchester City, Chelsea, Arsenal and Liverpool amongst the top-eight most valuable clubs.

Tottenham, Newcastle and West Ham complete the Premier League's representation.

Forbes' top 10 most valuable teams of 2015:
1 Real Madrid $3.26billion
2 Barcelona $3.16billion
3 Manchester United $3.10billion
4 Bayern Munich $2.35billion
5 Manchester City $1.38billion
6 Chelsea $1.37billion
7 Arsenal $1.31billion
8 Liverpool $982million
9 Juventus $837million
10 AC Milan $775million