Toni Nadal says there are four men in the French Open field capable of dethroning 10-time Roland Garros champion Rafael Nadal.

Uncle Toni, Rafa's original coach, returned to Paris to watch his nephew's match against German Maximilian Marterer today.

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Toni Nadal told ATP World Tour.com four players pose threats to the king of clay's reign.

"I'd say, besides Rafa, the most serious contenders are Novak Djokovic, Dominic Thiem and Alexander Zverev. The usual suspects," Toni Nadal said of the top contenders at Roland Garros. "And I'd throw Juan Martin del Potro into that group as well."

Two-time semifinalist Thiem surprised Nadal in Madrid last month.

"Dominic is the only player who has managed to beat Rafa in the past two years on clay," Toni Nadal said said. "He's a complete player with no glaring weaknesses and is tough to defeat."

Uncle Toni said Thiem is one of several top young talents in the sport.

"Dominic adapts well to clay, but the reality is you have to play well against all competition and on all surfaces," Toni Nadal told ATP World Tour.com. "Rafa is much more than [just a clay-court expert]. There are so many emerging talents right now in the game."

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