Guillermo Vilas says he is not impressed by Rafael Nadal's winning streak on clay even though the Spaniard will break the Argentine's record if he comes through his first round at the French Open on Monday.

The 19-year-old Nadal has been undefeated on the slow surface in his last 53 matches and looks set to add a 54th consecutive win when he kicks off his title defence at Roland Garros against Swede Robin Soderling.

"First of all, Nadal's performance is spanning over two years, which is not the same," Vilas, who set the record in 1977, told Reuters on Monday.

"Then, I have the feeling he added easy tournaments on his schedule just for that purpose," the 53-year-old added.

Vilas, who confessed he had to call the ATP to have confirmation of a record he had ignored, had his 1977 run ended in the Aix-en-Provence tournament semi-finals by Ilie Nastase.

"I did not lose to a player but against a racket," he said, referring to the double-strung racket the Romanian was using at the time.

"I could not play him. When I was 6-1 7-5 down, I threw in the sponge," said Vilas, who had won the Tehran, Bogota, Santiago and Buenos Aires tournaments that year.