Federer has won a record 16 Grand Slams, seven more than Nadal, and McEnroe isn’t ruling out the 29-year-old Swiss adding a “couple more” to that tally.

However, Nadal has a 14-7 record against Federer, and has won the Davis Cup title with Spain and an Olympic singles gold medal — two achievements that have eluded his rival.

McEnroe, speaking at the Aspire4Sport conference, said “there is an argument to be made that Rafael Nadal may be the greatest player eventually, even possibly now.” Former Swedish great Bjorn Borg said Federer is still the greatest though “Rafa has the chance to be the greatest player.”