US Open officials have fined Carla Suarez Navarro $US40,000 for violating the First Round Performance Rule.

The 30-year-old Spaniard retired after losing the first set of her opener against qualifier Timea Babos 6-2, citing back issues.

“After reviewing reports from Medical Staff and Grand Slam Supervisors, the determination was made that Carla Suarez Navarro did not perform to the required professional standards,” tournament referee Soeren Friemel said in a statement.

Suarez Navarro, the 28th seed, said on Twitter she had had “not the easiest weeks” this year due to back pain but did not directly refer to the fine.

“We made our best effort to be ready and play our heart out, but it got really worse during my opening match in New York,” she wrote.

“Sad to leave this way from events I deeply appreciate.”

Navarro isn’t the first to cop huge fines from tennis authorities.

Australia’s Nick Kyrgios was fined $167,000 for his spectacular meltdown in Cincinnati earlier this month.

Before that, compatriot Bernard Tomic was fined his full prize money of about $55,000 ($A80,000) at Wimbledon last month after a three-set loss in the first round that lasted only 58 minutes.