World number three Maria Sharapova's participation in next month's Beijing Olympics hinges on a scan on her right shoulder later on Thursday.
The injury forced the Russian to withdraw from the Montreal Cup despite a 7-5, 5-7, 6-2 win over Poland's Marta Domachowska on Wednesday.
"I think the (scan) results will help me with the bigger picture," Sharapova told reporters. "But at the end of the day it's tough to go on court and not be close to even 50 percent.
"I'm too good a player to go out there and try to fight through something I think can eventually become something serious."
Playing her first match since a shock second-round defeat by compatriot Alla Kudryavtseva at Wimbledon in June, Sharapova twice received treatment on her shoulder during her three-hour match in Montreal.
While her groundstrokes were crisp and powerful the Australian Open champion struggled with her serve, committing 17 double faults.
Sharapova said her shoulder had been troubling her since she played at Indian Wells, California in March.
"In the last few weeks I've been struggling with trying to find a solution to the aggravation I did to the shoulder back in Indian Wells," she said. "I haven't really found the solution yet.
"I spoke to a couple of doctors here. They advised me to try to find the cause of the problem."
The Olympics start on Aug 8.