Petkovic on Djokovic: "Anyone who doubts his level again should be condemned to eternal silence".

Andrea Petkovic still believes in Novak Djokovic. Despite the Serb's semi-final exit at the Australian Open against Alexander Zverev, the former German player wrote in her blog that Djokovic is a player not to be underestimated in the major titles, despite his recent physical problems.

"Anyone who doubts Novak's level of tennis again, whether he's 37 or 55, should be condemned to eternal silence.

Yes, I'm talking about myself. Not that I doubted his talent, but I didn't think he'd be able to retain enough explosiveness to keep up with the youngsters.

In Australia, I'd say he played really well in three games: against Machac, Lehecka and Alcaraz. He kept that consistency, but given his age, he hit the ball harder and changed direction more often.

This made him unpredictable in the eyes of his opponents. If he wants to win a 25th Grand Slam, his body will have to keep up.

For me, that's the only thing that's going to be a problem for him at 37. At that age, our strengths become weaknesses and then qualities again. It's the cycle of life.

But one thing's for sure: no one will ever doubt Novak's tennis again, no matter how old he gets. Years are just numbers in the rear-view mirror, but titles are forever," says Petkovic.