As long as Nadal is healthy, it's difficult to believe he won't find a way to win the tournament again when the best players in the world compete in Paris, beginning in late May and extending into June.
Nadal suffered a right-leg injury in the Australian Open that caused him to withdraw in the quarterfinal round, but it is not expected to have a long-term impact. He could be back after three weeks of rest, per Bruce Archer of the Express.
On the women's side, Australian Open champion Caroline Wozniacki deserves consideration, but if Serena Williams is healthy and hungry, there's little reason to think she will be beaten.
Williams is set to make her return in February in a Fed Cup match when the United States hosts the Netherlands in Asheville, North Carolina.
Wozniacki defeated Simona Halep 7-6 (2), 3-6, 6-4 to win the Australian Open and earn her first Grand Slam title Saturday, and while Halep was gracious after her defeat, she may have to wonder when her time is coming.
She made it to the final of the French Open last year, but she was upset in that match by unseeded Jelena Ostapenko.
"It's not easy to talk now," Halep said, per the Associated Press (h/t ESPN.com). "She played amazing. It's been a great tournament for me. I started not very well with the ankle injury. I just wanted to give my best every match, which I did. Of course I'm sad I couldn't win today, but Caroline was better than me."
Wozniacki was in tears at the end of the two-hour, 49-minute match. In addition to winning her first Grand Slam event, the Dane will move into the No. 1 spot in the rankings as a result of her victory. If Halep had emerged with the win, she would have gained the top spot.
"I'm never going to get the question again about being a world No. 1 without a Slam," Wozniacki said.
Federer appeared to be in some trouble after he dropped the fourth set and allowed Cilic to tie the match. However, the 36-year-old refused to succumb to his opponent's pressure or age and dominated the fifth set.
The Swiss won two majors in 2017, and he's started 2018 by taking the Australian Open. Federer won the Australian Open and Wimbledon last year, and his title in Melbourne this year is his sixth Australian open title.
"I'm so happy," Federer said, per the Associated Press (h/t ESPN.com). "It's unbelievable. Of course, winning is an absolute dream come true, and the fairytale continues for me. After the great year I had last year, it's incredible."
Federer has beaten Cilic in nine of their 10 career meetings.
Williams should be close to the top of her game by the time the French Open gets underway. There's no reason to think any of the other top women in the sport, including Wozniacki or Halep, can beat her when she is in form.
Perhaps they could challenge her and win a set, but it's difficult to see Williams losing once she has played in two or three tournaments.
No matter how well Federer is playing, it's even more difficult to see Nadal losing in the French Open. He basically owns that tournament, having won 10 times at Roland-Garros since 2005, and the French tennis fans welcome him as a conquering hero.
Perhaps Federer, Cilic or Stan Wawrinka could challenge him, but Nadal will not lose in Paris.