Felix Auger-Aliassime's Asian swing ended in disappointing fashion on Wednesday.
The Canadian retired with a knee injury while trailing 5-2 against Norway's Casper Ruud in the round of 16 at the Shanghai Masters.
The fourth-seeded Auger-Aliassime had won two three-set matches in a row before calling it early against the 20th-seeded Ruud.
Auger-Aliassime recently hired a new coach in Ivan Ljubicic, but their work may be on hold depending on the severity of the injury.
The Montreal native is projected to drop at least one spot from his No. 4 position when the new rankings come out next week.
Tennis Canada will be hoping Auger-Aliassime can recover for the Davis Cup Finals, Nov. 23-29 in Italy.
