The top two players in the world, Andy Murray and Novak Djokovic, both have something to prove as the pair return to the tour from injury to play this week's Monte Carlo Masters.
Both have been struggling with elbow injuries, but world number one Murray proved his fitness during a recent exhibition with Roger Federer in the Swiss city of Zurich.
Meanwhile, Djokovic showed good form in Davis Cup action last weekend, leading Serbia into the semi-finals.
"I feel great," the 29-year-old Serb said on Sunday's opening day. "It's nice to be in a place where I spend a lot of time training. It's home here. I spend a lot of time on these courts.
"It's normal for an athlete to go through (injury) ups and downs. I trust myself and the effort I put into my game. I have to believe I'll get the results I'm hoping for," added Djokovic, a two-time former winner of the event.
"All of my thoughts next week will be on this event, I won it in 2013 and 2015. I'm hoping this is the place to have a new start to the season."
Federer is the in-form man on tour at the moment, but the winner of three titles already this season is skipping the clay-court season curtain-raiser.
The prestige event in the Mediterranean principality could be another showpiece for Rafael Nadal, who will kick into gear on his favourite surface as he bids for an unprecedented 10th title at the Country Club overlooking the sea.
The fifth-ranked Spaniard has been pipped at the post so far in 2017 at the important moments, losing finals to revitalised rival Federer at the Australian Open and Miami while missing out on a title in Acapulco at the hands of American journeyman Sam Querrey.
"Monte Carlo is unique for me, I'm here to adjust my game and be ready to play," Nadal said. "The season has started well for me. I'm happy with how I'm playing.
"This is an historic event for me, I'm working to be ready. I'm excited to be here."
Nadal, 30, won his ninth title a year ago after a three-year gap, beating Gael Monfils in the final after dispatching Murray in the semis.
Monfils will be missing as he continues treatment on a knee injury which has bothered him for months.
Also missing is the injured Canadian Milos Raonic, Japan's Kei Nishikori and charismatic Australian bad boy Nick Kyrgios, who is delaying the start of his clay campaign after a strenuous Davis Cup effort in Brisbane.
France's Richard Gasquet is still recovering after appendix surgery.
Federer has said he will not play on clay until the French Open at Roland Garros in well over a month, taking advantage of his ATP privilege at age 35 to pick and choose his schedule with extra flexibility.
Murray and Djokovic take the top two seedings, with the tournament's top eight receiving byes into the second round.
The third seed is treble grand slam champion Stan Wawrinka of Switzerland, the 2014 winner, with Nadal seeded four.
Andy Murray (GBR x1)
Novak Djokovic (SRB x2)
Stan Wawrinka (SUI x3)
Rafael Nadal (ESP x4)
Marin Cilic (CRO x5)
Dominic Thiem (AUT x6)
Jo-Wilfried Tsonga (FRA x7)
Grigor Dimitrov (BUL x8)
Tomas Berdych (CZE x9)
David Goffin (BEL x10)
Lucas Pouille (FRA x11)
Roberto Bautista Agut (ESP x12)
Pablo Carreno Busta (ESP x13)
Alexander Zverev (GER x14)
Albert Ramos Vinolas (ESP x15)
Pablo Cuevas (URU x16)