Passler wants the temporary suspension to be lifted so that she can compete in the ongoing home Olympics.
She appealed the suspension to CAS. But, according to CAS, the 24-year-old should have first turned to the Italian anti-doping organization Nado. She can still do so before the deadline expires on Thursday, CAS said in a statement.
Passler tested positive at the end of January for the banned substance letrozole, which has been used by female athletes for weight loss and to treat breast cancer, among other uses.
The scandal shook Italy just days before the opening of Italy's home Olympics. The Italian biathlon team has rallied behind Rebecca Passler.
