Valencia - Top seed and three-time champion David Ferrer withdrew from the Valencia Open on Wednesday due to an elbow injury.
Ferrer, who claimed his fifth title of the year in Vienna on Sunday to edge closer to sealing his place at the World Tour Finals next month, was due to begin his campaign against German qualifier Daniel Brands on Thursday.
The Spaniard will be assured of his place in London as long as Richard Gasquet doesn't win the Swiss Indoors tournament in Basel this week and the Paris Masters next week.
Ferrer's withdrawal means Frenchman Benoit Paire is the only seed left in the top half of the draw after Australian third seed Bernard Tomic was beaten 3-6, 6-3, 6-4 by Uruguayan Pablo Cuevas.
Tomic was a set and a break up early in the second set before the world number 33 fought back and just one break of serve was enough in the decider to set up a quarter-final meeting with Portugal's Joao Sousa or Paire.
Britain's Aljaz Bedene is also out after losing 6-3, 6-4 to Canadian Vasek Pospisil.
American Steve Johnson, the runner-up to Ferrer in Vienna at the weekend, will face second seed Feliciano Lopez in the second round after defeating Slovakia's Martin Klizan 6-3, 6-4.
Roberto Bautista Agut edged an all-Spanish affair against Nicolas Almagro 7-6 (7/1), 4-6, 6-4.