Auckland - Spain's Tommy Robredo on Wednesday became the fourth seeded player to pull out of the Auckland Open tournament, citing a muscle strain.
A string of high-profile withdrawals has depleted the field at the warm-up event for next week's Australian Open, with organisers saying they were "disappointed" by world number 17 Robredo's departure.
Top seed David Ferrer, defending champion John Isner, French livewire Gael Monfils and now Robredo have all pulled out without hitting a ball in anger.
Robredo, who was seeded fifth, said he reluctantly withdrew after feeling an adductor muscle strain at the gym, saying he could not risk jeopardising his Australian Open campaign.
"I wouldn't be able to play good and the people would be disappointed, also it could make me worse for next week," he said.
"It's sad for me, I like to play here, they made a good effort to have a great tournament.
"Also, with other players pulling out of the tournament I wanted to push hard to not be another one, but sometimes it is what it is."
The tournament also lost world number 15 Roberto Bautista Agut but the Spaniard at least managed to play a set before retiring hurt after 40 minutes to give Frenchman Adrian Mannarino a 6-2, 2-1 armchair ride to the quarter-finals.
World number 13 Ernests Gulbis, the top seed in the weakened line-up, will play Czech Jiri Vesely later on Wednesday.