The Real Madrid forward’s 2016 earnings are listed as 88million US dollars (£70.5m) in the study, broken down into USD56m (£44.9m) in salary and prize money and USD32m (£25.6m) in endorsements.
His long-time rival as the world’s greatest player, Lionel Messi, comes in second in the list with USD81.4m (£65.2m), with NBA star LeBron James third ahead of Australian Open champion Roger Federer.
Five sports are represented in the top 10, with basketball’s Kevin Durant and Kobe Bryant and tennis star Novak Djokovic joining their rivals, golf represented by Phil Mickelson and Jordan Spieth and American football by Carolina Panthers quarterback Cam Newton.
Three-time Formula One world champion Lewis Hamilton is Britain’s highest-placed representative in 11th, one place ahead of Tiger Woods – the former world number one earned only USD274,000 (£220,000) in golf prize money but remained a marketable commodity with USD45m (£36m) in endorsements. Rory McIlroy is 17th in the list.
The NFL’s Dallas Cowboys topped the list of most valuable sports teams with an estimated worth of USD4.2billion (£3.37bn), with Real second and Barcelona third. The Super Bowl-bound New England Patriots and Premier League Manchester United complete the top five.
The overall Sports Money Index includes athletes, teams, brands and agencies and considers the links between them, with sportswear brand Nike ranked number one thanks in part to its associations with fourth-placed Barca, fifth-placed Ronaldo and sixth-placed James.
Forbes Sports Money Index 2016, top 20 athletes (earnings converted into pounds sterling)
1 Cristiano Ronaldo, football, £70.5m
2 Lionel Messi, football, £65.2m
3 LeBron James, basketball, £61.8m
4 Roger Federer, tennis, £54.3m
5 Kevin Durant, basketball, £45m
6 Novak Djokovic, tennis, £44.7m
7 Cam Newton, American football, £42.5m
8 Phil Mickelson, golf, £42.4m
9 Jordan Spieth, golf, £42.3m
10 Kobe Bryant, basketball, £40m
11 Lewis Hamilton, Formula One, £36.8m
12 Tiger Woods, golf, £36.3m
13 Eli Manning, American football, £36m
14 Joe Flacco, American football, £35.6m
15 Tom Brady, American football, £35.3m
16 Floyd Mayweather, boxing, £35.2m
17 Rory McIlroy, golf, £34.1m
18 Russell Wilson, American football, £33.5m
19 Sebastian Vettel, Formula One, £32.8m
20 Philip Rivers, American football, £30.4m
Top five most valuable teams
1 Dallas Cowboys, American football, £3.37bn
2 Real Madrid, football, £2.92bn
3 Barcelona, football, £2.84bn
4 New England Patriots, American football, £2.72bn
5 Manchester United, football, £2.66bn