Jannik Sinner said Saturday he was "very disappointed" but confident after the World Anti-Doping Agency (WADA) appealed the decision to clear him in his steroid case, seeking a ban of up to two years.

The Italian world No. 1 twice tested positive for traces of the banned substance clostebol in March but was exonerated and allowed to carry on playing.

The 23-year-old went on to win the U.S. Open earlier this month for his second major crown, weeks after the International Tennis Integrity Agency (ITIA) found he "bears no fault or negligence."