Monte Carlo - Roger Federer may not be playing at the Monte Carlo Masters but the Swiss legend was still at the forefront of 2018 finalist Kei Nishikori's thoughts on Sunday.

"Everything is possible (for Federer)," Asia's top player predicted.

Federer is due for a return to the dirt after two seasons completely off the surface in three weeks at Madrid, his lone scheduled tune-up prior to the French Open, which he last played in 2015.

"It (winning Roland Garros) might be tougher for him than winning the Australian Open or Wimbledon, but I'm sure he can do anything if he tries 100 per cent," said Nishikori.

"He's a lot different than anyone else on the Tour," added the world number three who lost the final here a year ago as Rafael Nadal won his 11th title in the principality.

"I'm sure Roger can do very well on clay. He's still my idol, he's the best player in history.

"I'm happy to see him playing more tournaments, I hope I can play him again," said the player who has beaten the 37-year-old Swiss three times and most recently last November at the year-end ATP Finals.

"He came from injury and won the Australian Open (2017). I'm sure he works harder than anyone else off court. I hope he does well," NIshikori said.

As for his own performance, the Japanese ace is optimistic after his 2018 showing in the Principality.

"I'm very happy to be back, I have good memories. Last year I gained confidence after coming back at this tournament from injury.

"I'm looking forward to playing this year. There are a lot of guys who are tough on clay, especially Rafa and Novak (Dkjokovic).

"I've loved playing on clay the last couple of years, I hope I can win the title. Winning a clay tournament is a big goal for me this year," said the two-time champion in Barcelona, Nadal's home event."

But he is certainly not taking Spain's king of clay for granted.

"This surface suits his game more and this event suits him even more than some tournaments on clay. It plays a lot slower and heavier, it's not easy for the opponent to hit a winner.

"I'm sure he feels confident playing here," Nishikori said of Nadal, who has been out for half a month trying to heal yet another problem with his left knee.

"But still, a couple of guys would have big chances to beat him."

Fifth seed Nishikori will open his campaign against the winner from Fernando Verdasco and Pierre Hugues Herbert of France.