Toni Nadal expects a grand slam title to prove beyond Roger Federer in 2019.
The Swiss extended his all-time men's record to 20 slam victories by winning the Australian Open in January but suffered some unexpected losses during the rest of the season, finishing it ranked third.
Nadal, the long-time former coach of his nephew Rafael, believes the physical demands of best-of-five-set test are likely to put the majors out of reach for 37-year-old Federer.
Writing in his column in El Pais, Nadal said: "What can we expect from 2019? I find it hard to see Federer lifting another grand slam cup.
"Obviously, I do not say it for his game, although I do say it for the toughness of the five-set tournaments. I have to confess that I said that on other occasions and the Swiss, repeatedly, surprised me."