Novak Djokovic & Rafael Nadal won't win more than 1 Slam combined in 2021: Consultant and coach Mats Merkel

Novak Djokovic and Rafael Nadal, the world's top two players, are widely expected to continue dominating the men's game in 2021.

17-time Major champion Novak Djokovic is the favorite to claim a record ninth Australian Open title next month, while Rafael Nadal is expected to win his 14th Roland Garros title in June. And the two are expected to be the top contenders at the two other Slams as well.

Rafael Nadal with the 2020 French Open trophy, which he won by beating Novak Djokovic in the final

But renowned consultant and former coach Mats Merkel is among those who believe that Novak Djokovic and Rafael Nadal will not dominate the 2021 Majors.

Merkel works for Adidas Sports Marketing, and has been associated with several prominent players in the past - including Dominic Thiem, Andy Murray, Ana Ivanovic and Caroline Wozniacki. In a recent interview, Merkel opined that we will see a more diverse winner's field at the Slams in 2021.

"It will be a very interesting year," Merkel said. "If all the four Grand Slams can be played regularly, I lean out the window and say that three of the four will not be won by Novak Djokovic or Rafael Nadal.

Dominic Thiem is the absolute showpiece model: Mats Merkel

Dominic Thiem wins the 2020 US Open

Mats Merkel expects the players outside of the Big 3 to continue moving forward in 2021, led by World No. 3 Dominic Thiem.

The Austrian broke through to claim his first Grand Slam at the US Open last September. He also defeated both Novak Djokovic and Rafael Nadal at the season-ending ATP Finals, before going down to Russia's Daniil Medvedev in the final.

Dominic Thiem is widely considered the biggest challenger to Novak Djokovic and Rafael Nadal at the moment, and Merkel thinks the same.

"It's going to happen, he's so good" - Davenport on whether Dominic Thiem can beat one of the Big 3 in a Slam final https://t.co/c3LOQAWo7R

— Sportskeeda Tennis (@SK__Tennis) January 11, 2021

"Dominic Thiem is the absolute showpiece model because he is constantly developing," Merkel said. "I am impressed by how he got out of the Corona era and won the US Open. It's a shame that he didn't end the year with a victory at the ATP Finals."

Merkel, who hails from Germany, also sees a lot of potential in countryman Alexander Zverev. However, Merkel believes that Zverev needs to fix the kinks in his serve to take the next step forward.

"Alexander Zverev has a lot of improvement areas, but great potential," Merkel said. "It starts with his serve. If he can get this under control and improve it, he will be able to position himself completely differently when it comes to the structuring of points."

Merkels went on to say that while he expected more from World No. 6 Stefanos Tsitsipas in 2020, he remains optimistic about the diverse talent in the men's game.

"Stefanos Tsitsipas played rather average for his standards in 2020," the German said. "But I'm still excited about all the guys. For me there are also Felix Auger-Aliassime, Grigor Dimitrov and Denis Shapovalov. Dominic Thiem also has reserves for how he can improve. He knows that too. And I'm impressed how the guys keep sitting down and thinking over how they can get better."