DOHA, Qatar (AP)—Roger Federer may have the most Grand Slam titles, but John McEnroe says Rafael Nadal is building a resume that could make him the greatest of all time.

Federer has won a record 16 Grand Slams, seven more than Nadal. Yet Nadal has a 14-7 record against Federer. Nadal has won the Davis Cup title with Spain and an Olympic singles gold medal—two achievements that have eluded Federer.

McEnroe, speaking at a sports conference in Doha, said “there is an argument to be made that Rafael Nadal may be the greatest player eventually, even possibly now.”

McEnroe adds that the 29-year-old Swiss star could add a “couple more” to that tally.

Former Swedish great Bjorn Borg said Federer is still the greatest, although “Rafa has the chance to be the greatest player” if he stays healthy.