Tennis fans have been debating the greatest coach of the 21st century, with the likes of Marian Vajda, Toni Nadal, and Patrick Mouratoglou in the conversation alongside many others.

Fans responded with great enthusiasm to a tweet by 'Swish' sparking off a debate about the best tennis coach of the 21st century so far.

"The important debate:

Who's the greatest tennis coach of the 21st century?," they wrote.

The post also featured a picture of five highly successful coaches; Vajda, Nadal, Mouratoglou, Ivan Lendl, and Magnus Norman.

Given the great achievements of all of these coaches, among many others, fans were divided on who they thought deserved the accolade.

"Toni [Nadal] or Vadja [Vajda], both have very strong cases," wrote one.

Spanish coach Nadal had an immense amount of success with his nephew, 22-time Grand Slam champion Rafael, who he coached for a majority of his career. The 64-year-old was the record holder for the most Grand Slams won as a coach until 2020, when he was overtaken by Vajda.

He now coaches Felix Auger-Aliassime and is the director of the Rafa Nadal Academy by Movistar.

Meanwhile, Slovak tennis coach Vajda worked with 23-time Grand Slam champion and current world No. 2 Novak Djokovic from 2006 until 2017, and then again from 2018 to 2022. In both 2010 and 2011, the 58-year-old won the award for best coach by the Olympic Committee of Serbia for his work with Djokovic.

Moreover, others supported the case for Mouratoglou.

"Moratoglou , what else!" wrote one.

The former French tennis player founded the Mouratoglou Tennis Academy in 1996, and has worked with several big names over the years. Most notably, he coached tennis star Serena Williams, helping her achieve her fifth, sixth and seventh Wimbledon titles, her fourth, fifth, and sixth US Open titles, her second and third French Open titles, her sixth and seventh Australian Open titles and an Olympic gold medal. 

The 53-year-old also worked with world No. 4 Holger Rune from October 2022 until April 2023, guiding him to his first ATP 1000 title at the Paris Masters, where he defeated Djokovic in the final. Mouratoglou currently works with world No. 7 Stefanos Tsitsipas.

However, others expressed their disappointment that other coaches weren't included in the original post's photo.

"Where's JC [Juan Carlos] Ferrero?", wrote one, bemoaning the absence of world No. 1 Carlos Alcaraz's coach.

"Sorry what is this Richard Williams erasure," added another, referring to the father of tennis legends Serena and Venus Williams, both of whom he coached for a significant part of their careers.