The shy-looking 23-year-old declined to comment as he entered the Court of Arbitration of Sport's (CAS) headquarters in Lausanne accompanied by his agent and legal team.

The former world top 10 player tested positive for cocaine during the Miami Masters in March and was provisionally suspended in May before serving a two- and-a-half month retroactive ban.

But an independent tribunal, appointed by the ITF, allowed him to resume his career in July.

The hearing on the appeal at CAS was expected to last a day, with a decision likely in about a month, an official said.