Federer holds the all-time record for Grand Slams won in the men’s division with 20.
Nadal is only three behind his Swiss rival but had he not been around then Federer may have added further to his tally.
That is according to Panatta, whose hypothesis would also take Federer beyond Jimmy Connors’ ATP trophy record of 109 – of which he is just eight away.
“Federer has fought against him and, without Nadal, he would have won 30 or 40 Grand Slams,” Pannatta said on his YouTube channel.
“Nadal is very polite and humble, and at the beginning of his career he had a lot of respect for Federer and he won.
“They are great friends and they are the most respectful guys in the whole circuit.”
Nadal is currently gearing up for the clay season, the surface in which he has dominated for well over a decade.
The world No 2 has a record 11 French Open titles and is the man to beat again this year.
That is so long as he overcomes a knee injury which ruined his American Sunshine Double swing.
Pannatta thinks Nadal has been so strong mentally that he drew comparisons with Bjorn Borg.
“Nadal is very good, he is the only one who has surprised me more and more in recent years, possibly being the best player in clay history,” he added.
“I have never seen a mentally strong player and I would compare him with Bjorn Borg.
“Like Nadal, he has also won Roland Garros and Wimbledon, but Borg retired with 26 years, while Rafa has continued playing.”
Nadal is back in action at the Monte Carlo Masters in a fortnight.
While Federer does not return until the Madrid Open in May.