Leading tennis players have returned negative results after their urine samples were re-tested for the newly-discovered steroid THG, the sport's governing body announced on Monday.

The International Tennis Federation (ITF) approved the retroactive testing of samples taken from the U.S. Open and Davis Cup plus out of competition tests in association with the World Anti-doping Agency (WADA) for tetrahydrogestrinone.

THG, a steroid tweaked by chemists to make it undetectable using standard tests, has been at the heart of a growing doping scandal that has rocked the sports world.

It was discovered in the U.S. earlier this year when an unnamed track and field coach sent the United States Anti-Doping Agency a syringe containing the substance.

The Olympic drug-testing laboratory at the University of Los Angeles identified it and developed a new test which has been rolled out worldwide to testing laboratories.