Sinner, the World No 1, withdrew after 20 minutes without winning a game, confirming he had felt unwell since the previous day.
Carlos Alcaraz expressed sympathy for Sinner, stating it was not how he wished to win the trophy and praising Sinner as a champion who would return stronger.
Sinner apologized to the crowd for the premature end to the match and congratulated Alcaraz on his sixth title of the 2025 season.
Sinner's fitness is now a concern ahead of his US Open defense, which is scheduled to begin on Sunday.