Federer currently has 19 Grand Slams to his name after winning the Australian Open and Wimbledon in 2017.
Nadal is Federer’s nearest challenger and he ensured the gap stayed at just three by winning the French and US Open.
At 36, Federer’s hopes of finishing on an insurmountable number are slim although he is the early favourite to win the Australian Open next month.
While Nadal, who is still the dominant player on clay, has more years to overtake Federer as long as his knees remain healthy.
And Henman says he wouldn’t be surprised if Nadal took the record.
Henman told Express Sport: “He’s got a chance hasn’t he. These are all opinions and the beauty of sport is that there’s no script and that’s why we watch it.
“If we knew what would happen, we wouldn’t watch it. And that’s another great question.
“Who’s going to be the next person to break into the dominance of the top four? Can Federer win more Grand Slams? Can Nadal overtake Federer?
“He could do. Who’s the favourite for the French Open next year, it’s gotta be Nadal by miles.
“So I wouldn’t be surprised if he did overtake Federer. But only time will tell.”