Rafael Nadal's former coach doesn't expect Roger Federer to win a grand slam title 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.
Toni 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."
Alexander Zverev's ATP Finals title last weekend, with the young German defeating Federer and Novak Djokovic back to back, provided a tantalising glimpse of what might be to come next season.
The long-awaited major breakthrough for the next generation appears at last to be around the corner, and Nadal admits he has been made to reconsider his opinion on the matter.
He said: "For some time I had my doubts about whether the youngsters would be able to overcome the game of Federer on grass, the one of Djokovic on fast courts and the one of Rafael on clay.
"And I had the impression that the change would be caused rather by the decline of some than by the attack of others. The final in London has made me think about it.
"For now, for the coming year, I trust in the full physical recovery of Rafael, I feel new episodes of his rivalry with Djokovic and, in general, a more open panorama with the definitive incorporation of the new generation."