"We have good reason to be optimistic," said one of his lawyers, Said Larifou, who said the case is "essentially political."
Sonko was struck off the electoral ballot after being sentenced in June to two years' imprisonment for morally corrupting a young person.
He has been at the center of a stand-off with the state that has lasted more than two years and sparked several episodes of deadly unrest.
Last month, the West African nation's top court overturned a regional ruling handed down in October, which had put Sonko back in the running for the presidential election.
The Supreme Court decided then that the question of whether Sonko should be restored to the electoral roll should go back to the lower court in Dakar.
Sonko denounces the cases against him as machinations aimed at keeping him out of the presidential election. The government denies any manipulation of the justice system.
The opposition figure was convicted in absentia on June 1, a verdict that set off the deadliest unrest Senegal has seen in years.
In July, he was arrested on other charges, including fomenting insurrection, criminally associating with a terrorist body and endangering state security.
He has periodically been on hunger strikes since then.
Sonko is particularly popular among Senegalese under the age of 20, who make up half the population, striking a chord with his pan-Africanist rhetoric and tough stance on former colonial power France.
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