Serbian tennis legend Radmilo Armenulic believes Novak Djokovic has made a mistake in ditching coach Marian Vajda.
Djokovic and Vajda were arguably the most successful player and coach partnerships in tennis history.
Under the guidance of the Slovakian, Djokovic won 85 ATP titles and 20 Grand Slams in 15 years together.
They decided to part ways at the end of last year, with Vajda reportedly frustrated at sharing coaching responsibilities with Goran Ivanisevic.
It is not the first time they have split, with Djokovic also losing Vajda in 2017, with the most unsuccessful period of his career following.
That is why Armenulic believes his compatriot has made an error in allowing Vajda to walk away, telling Serbia news outlet Kurir: "I think he misses Vajda!
"With him, Novak achieved better results, [and] he was mentally more stable.
"Ivanisevic is a new coach; he has no experience. He can share advice, but Vajda was more specific, convincing, [and] closer. That meant a lot to Djokovic because he is emotional."
Djokovic is currently playing the Rome Masters, where a run tot he semi-finals will guarantee him the top seed for Roland Garros.
Anything less, according to Armenulic, should be considered 'failure'.
"Novak is the world number one," Armeulic said. "If he doesn't win a tournament or doesn't make it to the finals, it's a failure.
"If he is not the first seed at Roland Garros, he will be in trouble. Why? Well, because more serious opponents would be waiting for him in the third round.
"He is mentally stable but, in my opinion, physically unprepared. He needs to work on his condition to stay number one.
"He must have strength for the third set or, in Paris, for the fifth. He has a team that takes care of that. I believe they will prepare him."