Pakistan, Nov. 9 -- Elena Rybakina's withdrawal from the WTA Finals on the eve of the season-ending championships is disappointing, but the world number one needs time to recover from the physical toll of a demanding year, tournament director Garbine Muguruza said.

Defending champion Rybakina pulled out of the tournament on Saturday, saying she was not physically ready to compete, leaving Ukraine's Marta Kostyuk to take her place in the eight-player field at Indian Wells. Tournament organizers later said a viral illness was the official reason for the withdrawal.

Muguruza, the former world number one and two-time Grand Slam champion, said she had spoken with Rybakina and that the Kazakh had been unable to recover in time after strugglin...