Mischa Zverev believes the key to beating Rafael Nadal on clay is to take him deep, while Boris Becker feels the Spanish great does not look as strong as last year.
Nadal is putting the finishing touches to his build-up for the defence of the French Open, but things have not been as smooth as recent years.
The 13-time Roland Garros winner opened his clay campaign with a surprise loss to Andrey Rublev in the quarter finals of the Monte Carlo Masters, before claiming the Barcelona Open title for a 12th time.
Djokovic can play in French Open without a vaccine - sports minister
His bid for victory in Madrid was derailed by Alexander Zverev, Mischa's brother, but he avenged that loss to reach the semi-finals of the Italian Open on Friday.
Nadal will look to fine tune his game ahead of the start of the French Open, which gets underway on May 30, but Mischa Zverev and Becker feel the 34-year-old could be vulnerable in Paris.
Speaking on a Eurosport podcast about the secrets to beating Nadal, Mischa Zverev said: “You have to be strong in your head, be confident and believe in your own game. And you have to know exactly how to beat him. Tactics are very important against Nadal.
As soon as you feel like you want to fight Nadal's forehand with your own forehand, you don't have a chance, because Rafa's forehand is just more dangerous on clay, has more spin and everything.
“You have to firmly believe that your tactics are right. You have to use these tactics and always try to make the right decision on the court - and if possible over five sets.
“Then you can hope that Nadal gets nervous. That can happen in five-set matches - maybe less so in Paris, but I've seen it happen on other courts. That's when he misses his forehand twice at 4:4 and 30:30 in the fourth or fifth set, if you've made him get nervous at that point and think about his game.
"Only when the others are so good that Rafa no longer dares to play certain shots faster or closer to the lines, then he starts to think.
“Example [Stefanos] Tsitsipas: If Rafa knows that Tsitsipas' weakness is his backhand, he will confidently work on his backhand until it collapses. Now, however, Tsitsipas is moving much better this season.
“So Rafa has to be more careful how he plays his own forehand, because if it's not perfect, Rafa suddenly has the problem. In this way, the gap between Rafa and the other players on clay shrinks.
“That can happen this year and Sascha (Alexander Zverev] is someone who can cause that in my eyes."
Nadal triumphs in thriller over Shapovalov in Rome
Becker, a six-time grand slam champion, feels Nadal’s air of invincibility on the red clay of Roland Garros may have deserted him in 2021.
“Nadal has a passport and it says age 35 from June,” Becker said. “Let's talk about Nadal 2020 for now: I've never seen him as strong as he was in last year's French Open final against Novak Djokovic. But tennis is fleeting, only the next match counts.
This year I haven't seen him as strong on clay as last year. Mischa spoke about self-confidence: If he doesn't win Rome now either, he can't come to Paris with an incredible amount of confidence.
“Yes, he has won the tournament 13 times, but I didn't find him that dominant yet this year. Even in Barcelona he had to go over three sets - he didn't win that as dominantly as he has in the past.”
'I'm very proud' - Mauresmo becomes first female tournament director of Roland Garros
The moment Federer closed out epic comeback against Haas at 2009 French Open