Rafael Nadal believes that facing Roger Federer at the US Open might have to remain an intriguing fantasy after the worrying decline of the Swiss superstar continued in New York.

Federer, winner of a record 17 Grand Slam titles, fell to Spanish 19th seed Tommy Robredo on Monday.

The result also doomed hopes for a potential quarterfinal match with 12-time major winner Nadal in what would have been the first meeting at Flushing Meadows in the pair's 31-match rivalry.