Medvedev feels Carlos Alcaraz slow down inevitable as pair start ATP Tour finals

A few months later, however, 24-time Grand Slam champion Djokovic has re-asserted his authority and Alcaraz is experiencing the first slump of his career.

He bemoaned the fast playing conditions in Turin after a surprise loss to Germany's Alexander Zverev (26) in his opening match at the ATP Finals on Monday.

Daniil Medvedev (27), whose defeat of Alcaraz in the US Open semi-final exposed some cracks in the Spaniard's game, says that a dip was to be expected at some point.

"If you would ask me two or three months ago, for sure (I would be surprised)," the Russian told reporters after his opening victory against compatriot Andrey Rublev (26).

"Now? You know, tennis is a very, very tricky sport. And at this moment, for whatever reason, we feel that Carlos plays just a little bit slower. He does not have the same confidence he had throughout the whole year.

"This can happen to everyone. This even happened to Novak when he was younger. The question is, how fast is he going to recover? Is it going to be in this tournament or next year?"

Alcaraz will face Rublev in Red Group on Wednesday when defeat could end his hopes of reaching the semi-finals.

He is looking to become the youngest ATP Finals champion since Pete Sampras in 1991.

While Alcaraz's recent defeats have raised eyebrows, fellow Spaniard Alex Corretja, an analyst for Eurosport, says those reading too much in to his form are mistaken.

"I think the summer, it was too demanding for him and it was difficult for him to deal with all the expectations and all his motivation maybe to finish number one knowing it was a high expectation," he said.

"But nothing is wrong with Carlitos. Carlitos is great."