Carlos Alcaraz says he "preferred" to retire from his Paris Masters quarter-final than risk further damage to an abdominal injury before the ATP Finals.
It leaves the Spaniard with a fitness concern just days before next week's season-ending ATP Finals in Turin.
"I cannot stretch. I couldn't serve well, I couldn't hit the forehand well," said US Open champion Alcaraz.
"I preferred to retire, see the extent of it and take care.
"I'm focused on trying to get better in the abdominal and trying to be at 100% [for the ATP Finals] in Turin."
Alcaraz is set to make his debut at the eight-man ATP Finals, which is indicative of his rise over the past 12 months.