The Court of Arbitration for Sport [CAS] has begun hearing an urgent appeal by the provisionally suspended Dayana Yastremska so a decision can be taken about her participation at next month's Australian Open.
Ukraine's Yastremska was suspended earlier this month after the World Anti-Doping Agency [WADA] found a banned substance in an out-of-competition urine sample she submitted.
The International Tennis Federation [ITF] had denied Yastremska's application to have the suspension lifted even as the world No 29 was preparing to compete in the year's first Grand Slam, which begins on 8 February in Melbourne.
"The CAS arbitration has commenced and the parties have agreed to an expedited procedure in order to enable a sole arbitrator to issue a final decision by 3 February," the CAS said in a statement.
Yastremska, who travelled to Melbourne and is currently in quarantine, had denied using performance-enhancing drugs and said the positive test was the result of a "contamination event".