New York - Spain's Carla Suarez Navarro has been fined $40 000 (R609 918) by the US Open for lack of effort in her first-round match against Hungarian qualifier Timea Babos, tournament referee Soeren Friemel said.
Suarez Navarro, a US Open quarter-finalist last year, matching her best Grand Slam run, retired at the end of the first set with a lower back injury.
The 30-year-old, who reached the fourth round last month at Wimbledon, won her only WTA titles at the 2014 Portugal Open and 2016 Qatar Open.
Grand Slam rules outline a code of conduct for performances in first-round matches, with players expected to perform to "a professional standard."
"After reviewing reports from the medical staff and the Grand Slam supervisors, the determination was made that Carla Suarez Navarro did not perform to the required professional standards," Friemel said in a statement.
She could have been fined up to the full $58 000 she received for a first-round loss at the year's final Grand Slam event.