Maria Sharapova's meldonium hearing may not take place until June, says Shamil Tarpishchev, the president of the Russian Tennis Federation (RTF).
It was revealed in March that the Russian failed a drugs test at the Australian Open in January, with meldonium having been added to the banned substance list at the start of the year.
Sharapova claimed she had been taking meldonium for health reasons and was not aware it had been placed on the prohibited list.
She was subsequently suspended, and a hearing into the matter was reportedly expected to take place this week.
However, RTF chief Tarpishchev has cast doubt on a swift conclusion, explaining that the matter is not a straightforward one.
"Sharapova's situation is complicated," he told TASS. "The thing is that she admitted that she had taken meldonium.
"The case will not be considered so long as the two laboratories do not study the preparation. I believe that's not going to happen earlier than June."