World No 13 Gulbis, who had been aiming to get some valuable time on court ahead of next week’s Australian Open, was beaten??6-2 3-6 6-1 by Czech qualifier Jiri Vesely.
Gulbis was promoted to top seed after David Ferrer withdrew before the tournament, and Ferrer’s Spanish compatriot Robredo followed him in pulling out before he hit a ball.
Robredo was due to play Michael Venus but he was replaced by qualifying lucky loser Lucas Pouille, who made the most of his late call and beat the New Zealand professional 7-5 6-4.
“I wouldn’t be able to play good and the people would be disappointed, also it could make me worse for next week,” Robredo said.
“It’s sad for me…but sometimes it is what it is.”
Gulbis was not the only seed to fall on Wednesday, with Spain’s Robert Bautista-Agut withdrawing from his match against Adrian Mannarino when he was down 6-2 2-1.
Last year’s finalist Lu Yen-Hsun of Taiwan departed after a meek 6-2 6-4 loss to Albert Ramos of Spain, leaving only Kevin Anderson and Steve Johnson as seeds in the quarter-finals.