Canadian Milos Raonic withdrew from his quarter-final match against top seed Jannik Sinner on Friday in Rotterdam.
Raonic trailed 7-6 (4), 1-1 when he left the match, having won his serve in the second set.
The 33-year-old Raonic returned to the ATP Tour last year after a prolonged absence due to injury.
The former world number 3 was looking to qualify for his first semi-final since the Paris Masters in 2020.
Raonic, who arrived in Rotterdam at 309e world rank, showed some of his optimal form against Sinner, fourth racket in the world.
The Ontarian scored 11 aces against Sinner before withdrawing from the match.
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