Griner, a two-time Olympic gold medallist who played professional basketball in Russia, was detained at a Moscow airport in February days before the country's invasion of Ukraine.
The athlete was charged with drug smuggling for possessing vape cartridges with cannabis oil and faces a possible 10-year prison sentence.
She made a court appearance in the Moscow suburb of Khimki on Tuesday.
Alexander Boykov, a lawyer for Griner, told reporters she would “probably” be cross-examined on Wednesday.
Mr Boykov said her defence team is hoping for a lenient sentencing, citing “a lot of extenuating circumstances”.
He added that Griner only used cannabis “occasionally” to relieve pain and that she had permission from an American doctor to use it for medicinal purposes.
“We are not arguing that Brittney took it here as a medicine. We are still saying that she involuntarily brought it here because she was in a rush,” Mr Boykov said after the session in which a Russian neuropsychologist gave evidence about the worldwide use of medicinal cannabis.
Maria Blagovolina, a lawyer, added: “With the prescription in place, Brittney may have used it for medical but not recreational purposes.”
Griner listened to the proceedings via a translator. Before sitting in the defendant's cage, she held up a piece of paper with pictures of her two best friends and her wife, Cherelle, wearing her number 42 jersey, the number she wears when playing for her WNBA team, the Phoenix Mercury.
Elizabeth Rood, the US embassy chargé d'affaires, told reporters that Griner was “doing OK and as well as can be expected”.
US officials have designated Griner as “wrongfully detained” and demanded her immediate release. Moscow claims the case has nothing to do with politics.
President Joe Biden said he has spoken to Griner's wife and called it a “priority” to bring her back to the US.
Agencies contributed to this report