And of course, the top-seeded Andy Murray can not be overlooked.
Rafael Nadal's red-hot form makes him the favourite at Roland Garros when the French Open begins on Sunday and Murray told AFP in Paris: "Maintaining your motivation, your focus and concentration for a very long period is hard".
The 20-year-old Alexander Zverev beat Novak Djokovic to win the Italian Open on Sunday, while the 23-year-old Dominic Thiem also impressed in the tournament, defeating Rafael Nadal. Sharapova's ranking wasn't high enough to gain direct entry into the tournament as she returns from a 15-month drug suspension, and the head of the French Tennis Federation decided not to give her a wild card.
The world number one will begin his bid for a fourth Grand Slam title against the 85th-ranked Russian, against whom Murray has won both matches. "It's a big change that I've experienced in the last three, four weeks, separating from the team I was with the last 10 years", Djokovic said. "Their level of tennis is quite fantastic". Rafa is playing on his favourite surface and playing with confidence, much better than past year. Federer, 35, chose to skip the entire clay-court season to prepare for grass at Wimbledon.
There was something unsettling about watching Nadal being thrashed by Djokovic in the 2015 quarter-finals, only his second ever loss at the slam he has owned since 2005.
Djokovic, who lost his No. 1 ranking to Murray a year ago, has won only one of his last 11 tournaments.
The Serb finished 2016 at No. 2, his current ranking, and has won only one of his last 11 tournaments. "That's one of the things I felt like I needed is new inspiration, someone that knows exactly what I'm going through on the court, off the court".
"Andre had a renaissance later in his career, into his 30s where he had success late in his career", McEnroe, who will be imparting his wisdom for Eurosport during the French Open, said.
"Potential danger lurks in round three in the shape of 29th seed Juan Martin del Potro, should he recover from injury problems in time", adds the paper.
The 47-year-old Agassi will not stay in Paris for the duration of the French Open.
Simona Halep, the 2014 runner-up, established herself as arguably the leading challenger by winning the Madrid Open before reaching the Rome final, but an ankle injury has cast doubt over her status.