Endore this: These sports stars make big money through endorsements

In modern day sports, eye-popping multi-million contracts are fairly commonplace. What sometimes goes unrealized, however, is that a number of big name sports players make their biggest money off the court or field—namely through lucrative product endorsements. 

As a result, big contracts with sports organizations are no longer the only way to bring home the bacon. For many athletes, building a brand and public image is an essential step towards earning even bigger paydays with big retail and apparel companies. And make no mistake: A brand endorsement contract is a very big payday indeed. Through endorsement deals, some athletes make almost double what they make in their sports earnings. 

After being retired for more than a decade—well past his earnings prime as an athlete—basketball great Michael Jordan raked in an estimated $100 million through endorsements in 2015, a testament to how powerful a personal brand can be when it has the backing of a corporate brand. Using estimates from various publications, CNBC looks at the endorsement earnings of a handful of marquee sports figures at the top of their game, both in sports and money.

Ever since winning his first singles Grand Slam tournament in 2003, tennis legend Roger Federer has been perfect on both on and off the court. The 17 time Grand Slam singles champion is regarded to as the greatest tennis player of all time and that has translated into big endorsement dollars. It has been four years since Federer won his last Grand Slam, but he is still one of the most highly paid athletes in the world: The Daily Mail recently estimated the Swiss star earns about $58 million in agreements with Wilson, Nike, Rolex and Mercedes Benz, among others.

Deciding to skip college and enter the NBA draft proved to be a lucrative financial decision for the Akron Ohio native. At the age of 18 years old, James inked a colossal $90 million eight year deal with Nike—a deal GQ recently suggested may be worth more than $1 billion as part of a lifetime deal the company inked with James. 

Now 31, the four-time NBA MVP and recent MBA champion has a net worth estimated to be over $300 million. That figure is likely to grow now that he's opted out of his current contract with the Cleveland Cavaliers, en route to either another team—or an even bigger payday with the Cavaliers.

Not having won a major golf tournament in about 3 years hasn't done much to dent Phil Mickelson's earnings power. Mickelson is currently the PGA's highest paid golfer and is making a whopping $50 million a year from endorsements, according to Money Nation. "Lefty" has more than five sponsorships that vary from diverse brands like KPMG, Barclays, Rolex and Amgen. 

No longer ranked among the world's elite golfers, Tiger Woods is still collecting endorsement money that keeps him among the world's highest paid professional athletes. At the age of 19, Woods accepted a five year, $40 million deal with sports juggernaut Nike, and the two parties are still working with one another after more than 20 years. Now 40 years old, Wood's career has come to a screeching halt both on the green and in regards to sponsorship.

That doesn't mean, however, that he's still not raking in the cash. In 2014, Golf Digest reported that Woods pulled in about $1.3 billion in career earnings, and the publication recently ranked Woods as golf's 3rd best paid athlete with $48.5 million made last year. His most lucrative deals are with Nike and Rolex.

After finishing his 9th season in the NBA, Kevin Durant has found his footing in the endorsement world. Durant made a huge splash in 2014 after being elected the NBA MVP with a 10 year, $300 million deal with Nike. The four time scoring champion currently has over 12 sponsorships, varying from Beats headphones to Sparkling Ice, and recently just came out with his new NIke shoe line, the KD 8 EXT "Floral Finish." 

Currently the star small forward has more than 12 endorsements and is making $36 million through sponsorships this year. 

Only 27 years old, Rory McIlroy has been one of the most dominant golfers in the world. In 2014, Rory was placed in a selective group of only three people to win three majors by 25; the other two golfers are Jack Nicklaus and Tiger Woods. The Northern Irish golfer has signed multiple endorsement deals including ones with Bose and Omega. 

Rory added onto his list of sponsorships in 2013, when Nike offered the phenom a $200 million, multi-year contract. Just through endorsements the young golfer is currently making more than $37 million per year, Golf Digest estimated recently.

Currently the defending champion in every Grand Slam Single tournament is 29 year old Novak Djokovic. In 2014 the Serbian became the first player in tennis history to earn $20 million in a single season and jumped into the mix with Roger Federer to become the first tennis player to pass $100 million in earnings without bonuses. After winning a dozen Grand Slam Singles titles, Djokovic has sponsorships with ANZ and Seiko but the majority of the tennis star's sponsorship earnings come from Adidas and Uniqlo—a company with whom he just signed a $50 million extension.