Germany's Tommy Haas blamed the effects of hayfever for his withdrawal from his first-round match against Robin Soderling at the Hamburg Masters.
Haas said he had problems with his breathing during the match
Haas was trailing 6-2 2-1 when he decided to come off court, much to the displeasure of some of the German fans.
"As soon as the match started and I realised I didn't feel well, I got sort of a panic attack," said Haas.
Meanwhile, Sebastien Grosjean upset 14th seed Robby Ginepri 7-5 7-5 and Nikolay Davidenko beat Nicolas Massu.
Former French Open winner Gaston Gaudio overcame Spain's Alberto Martin 6-2 3-6 6-4, and the Argentine was not shy about his chance in the tournament following the withdrawal of Roger Federer and Rafael Nadal.
"Of course, Nadal and Federer pulling out is so much better for us," said Gaudio.
"For me, I have a pretty good chance to win the tournament or to reach the semis."