Federer will face a "reality check" when he returns to the Tour after a lengthy injury break, seven-time major champion Mats Wilander said.
Nadal returned to the top of the world rankings on Monday after winning his eighth Italian Open title to confirm again his status as the king of the clay court.
Nadal's Australian Open quarter-final curse struck again on Tuesday, an injury forcing the top seed to retire in the fifth set against Croatia's Marin Cilic.
World number one Rafa Nadal dismissed Dusan Lajovic 7-6 (6) 6-2 6-2 to ease into the U.S. Open second round on Tuesday.
Second seed Djokovic's fourth-round match against France's Adrian Mannarino was pushed back from Monday due to the epic five.
Home fans will be treated to a double-bill of British number ones at Wimbledon on Wednesday.