Rafael Nadal's uncle and former coach, Toni Nadal, feels it will be tough for the Spaniard to replicate his 2017 success next year.
The 31-year-old left-hander took his major tally to 16 this year with victories in both the French Open and at the US Open while he also returned to the top of the world rankings.
It was a remarkable turnaround for the Majorcan, whose career looked in jeopardy after loss of form and a number of injuries had seen him slip down the rankings.
The challenge now is to keep it going and the man who coached him for 27 years, before handing the reins to Carlos Moya and Francisco Roig, believes the return of a few key players will mean it will be difficult for his nephew to dominate proceedings once again.
"This year has been it happens that Djokovic has not been at his best and Murray either," Toni Nadal told Spanish newspaper ABC. "And (Stan) Wawrinka, (Kei) Nishikori and (Milos) Raonic have also had problems.
"Next year it will be difficult to win many titles, although I hope Rafael continues to prove he is the best on the clay and win again Monte Carlo, Barcelona and Roland Garros."