Canada's world number seven Eugenie Bouchard withdrew from the debut season of the International Premier Tennis League (IPTL) on Thursday with an injury sustained in training.
The 20-year-old was due to be part of the UAE Royals team at the four-city tournament, which begins in Manila on Friday.
Bouchard "has been forced to withdraw from the league due to an injury she sustained in training on Monday," said a statement released in Singapore by the tournament organisers.
An IPTL spokeswoman told AFP she could not immediately comment on the nature of the injury, sustained during a training session on Monday.
"I'm really disappointed I will be unable to compete in the IPTL this year due to an injury that I recently suffered in practice," Bouchard said in the statement.
France's 21-year-old Kristina Mladenovic will take Bouchard's place in the UAE Royals, which also features Novak Djokovic and Caroline Wozniacki.
The team is up against the Manila Mavericks headlined by Andy Murray and Maria Sharapova on Friday.
The three-week long IPTL, which also features Roger Federer and Serena Williams, will be played in Manila, Singapore, New Delhi and Dubai.
Teams representing each of the four cities will play each other in each venue in a mini-league with an adventurous format: team ties consisting of five one-set matches, with no advantages and the first to six games wins.
Play at the inaugural tournament will also be dramatically shortened by a 20-second shot-clock between points and the stipulation that at 5-5 players go into a timed shoot-out in which they must accumulate the most points before time is up.
Players can also call a "power point" once per set, meaning the next point will count double.
Source: AFP