Novak Djokovic was forced to retire from his Dubai Tennis Championships quarter-final against Feliciano Lopez.
The world number one suffered from an eye problem and quit after losing the first set 6-3.
A day on from his 700th career win, Djokovic's run of making 17 successive Tour finals came to an end after making 18 unforced errors in only nine games against the sixth seed.
"It started with an infection and then severe allergy," said Djokovic.
"I have had it ever since I arrived in Dubai. It's gotten worse in the last two days, unfortunately. It's the first time that I have had such a problem with the eye. It was ultra-sensitive today."
Spaniard Lopez will now face Cypriot Marcos Baghdatis in the semi-finals.
Djokovic, an 11-time major champion, has won the Dubai Championship four times previously.
Playing in his first tournament since winning a sixth Australian Open title at the end of January, the Serb uncharacteristically lost his opening service game and had to save three break points to avoid falling 3-0 behind.
The 28-year-old then called for his trainer, before continuing the match.
Six games later, after being broken once again to lose the set, Djokovic said he was unable to continue.
Lopez said: "It's very sad when one of the greatest players ever has to retire from a match like that"