More than four months after she was first detained, the W.N.B.A. star Brittney Griner is expected to appear in a Russian courtroom on Friday for the start of a trial on drug charges that legal experts said was all but certain to end in a conviction despite the clamor in the United States for her release.

“There’s a bias mainly because the Russian judicial system says they really should not go to trial unless the defendant is going to be convicted,” said William Pomeranz, the acting director of the Kennan Institute and an expert on Russian law. “There’s no real idea or expectation that the defendant could be innocent. There’s no presumption of innocence, really.”

Russian customs officials said they found vape cartridges containing traces of hashish oil in Griner’s luggage when she passed through a security checkpoint in an airport near Moscow on Feb. 17. The drug charges that Griner faces carry a sentence of up to 10 years at a penal colony.

Aleksandr Boikov, Griner’s lawyer, said on Monday that he expected the trial to begin on Friday and last up to two months.

“We do not know at this point what evidence they have,” Pomeranz said. “We don’t know how many volumes of evidence they want to read into the record, but usually, in this type of case, it’s formidable and significant.”

Griner’s detainment arrives at a delicate geopolitical moment during Russia’s ongoing invasion of Ukraine and amid Russia’s strained diplomatic relationships with the United States and some European countries. From the start of Griner’s detainment, her supporters feared that she could be used by Russia during the global conflict.

In May, the U.S. State Department affirmed those concerns by declaring Griner had been “wrongfully detained.” That shifted responsibility for the case to the government bureau that leads and coordinates the United States’ diplomatic and strategic efforts on overseas hostage cases.

“Brittney has been classified as wrongfully detained since April 29, which means that the U.S. government has determined she is being used as a political pawn and as a result, is engaging in negotiations for her release, regardless of the legal process,” Griner’s agent, Lindsay Kagawa Colas, said in an email on Wednesday. “As such, our expectation — Brittney’s family included — remains that President Biden get a deal done to bring her home.”

Griner’s family and supporters are increasingly imploring President Biden and the U.S. government to secure Griner’s release.

Kagawa Colas recently coordinated a letter to Biden and Vice President Kamala Harris signed by groups including the National Organization for Women, the Human Rights Campaign, the National Urban League and the National Action Network. The letter called for the government to strike a deal for Griner’s release.

In April, Russia, after agreeing to a prisoner exchange, freed Trevor Reed, a former U.S. Marine who was sentenced to nine years in prison after being accused of endangering Russian police officers during an altercation.

Reed’s deteriorating health in Russia most likely played a factor in Moscow’s willingness to release him, said Kimberly St. Julian-Varnon, a Ph.D. student in the history department at the University of Pennsylvania, whose areas of study include African American experiences in the Soviet Union, Ukraine and Russia.

“The problem is Brittney, politically, is worth so much more in terms of the trading of prisoners than Trevor Reed because of her profile. So the ask is going to be much bigger, and I think the ask that they’ve been telegraphing in the Russian news is for Viktor Bout,” said St. Julian-Varnon, who has consulted with the W.N.B.A. players’ union about Griner’s detainment.

Bout, an international arms dealer, was convicted by an American court and sentenced to 25 years in prison. Russia also has interest in freeing Roman Seleznev, a hacker who was convicted in the United States for running a massive credit card and identity theft operation and sentenced to 27 years in prison. Besides Griner, Russia has also detained Paul Whelan, a former U.S. Marine sentenced to 16 years on espionage charges.

“This is the classic dilemma of hostage situations,” said Thomas Firestone, a former Justice Department official who worked in Moscow as a lawyer. “If you negotiate for the release, you may be encouraging future hostage taking. If you don’t, the person may never be released.”

Jake Sullivan, Biden’s national security adviser, told reporters on Tuesday that he and Secretary of State Antony Blinken had spoken to Griner’s wife, Cherelle Griner, in recent days.

“The United States government is actively engaged in trying to resolve this case and get Brittney home,” Sullivan said. He added: “It has the fullest attention of the president and every senior member of his national security and diplomatic team. And we are actively working to find a resolution to this case and will continue to do so without rest until we get Brittney safely home.”

On Tuesday, Russia announced it had barred Biden, the first lady, Jill Biden, and others from entering the country in response to far-ranging sanctions. The list included four senators: the Republicans Mitch McConnell of Kentucky, Susan Collins of Maine and Ben Sasse of Nebraska and the Democrat Kirsten Gillibrand of New York.

“Free Brittney Griner,” Sasse said in a statement. “It’s no big deal when Putin throws a tantrum and bans Americans from Russia — but we’ve got a problem when he takes an American prisoner.”

Griner is one of the world’s most decorated basketball players — a seven-time W.N.B.A. All-Star, two-time Olympic gold medalist and the first openly gay athlete signed to an endorsement contract by Nike. She traveled to Russia after a two-week break to play for UMMC Ekaterinburg, a powerhouse professional women’s basketball team.

Updates on Griner since have been scarce and mostly parceled out by Russian state media. Griner has communicated with W.N.B.A. colleagues through letters and emails, according to The Associated Press. But Cherelle Griner told The A.P. that a recent long-planned phone call between the two did not occur because of a logistical error at the U.S. embassy in Moscow.

“I find it unacceptable, and I have zero trust in our government right now,” Cherelle Griner told The A.P. in late June. “If I can’t trust you to catch a Saturday call outside of business hours, how can I trust you to actually be negotiating on my wife’s behalf to come home?”

In a radio interview Wednesday with the Rev. Al Sharpton, who also is the founder of the National Action Network, Cherelle Griner said she hadn’t spoken with her wife since February but had received letters.

“She’s telling me she’s OK,” Cherelle Griner said of her wife’s letters. “She’s like, ‘I’m OK, babe. I’m hardened. I’m not me right now. When I come home, it’s going to take me a minute to get back to myself, but I’m holding on. I won’t break until I come home. I won’t let them break me. I know they are trying to, but I’m going to do my best to just hold on until I can get home.’”

Paris Hatcher became more dismayed after learning of Brittney Griner’s detention being extended on Monday and seeing a picture of Griner circulated by Russian state media.

“She looks scared,” said Hatcher, whose organization, Black Feminist Future, created a #BringBrittneyHome online campaign: “The big piece around this is there’s somebody who’s been detained. This is around dignity. This is about someone’s humanity. She deserves to be connected to her family.”

The rights of those accused in Russia contrast sharply with someone charged with a crime in the United States, St. Julian-Varnon said.

“You don’t have a right to a trial by jury,” St. Julian-Varnon said. “You do not have a right for your lawyer to call whatever witnesses they want. The entire case against you and the case supporting you comes from evidence collected by the state.”

Still, St. Julian-Varnon said she remained cautiously optimistic that Griner might eventually be released either through a prisoner exchange or by being convicted on a lesser charge and agreeing to pay a sizable fine.

“There’s a lot of moving pieces,” St. Julian-Varnon said. “I want to remain optimistic, because it’s still her life. It’s Brittney’s life. It’s Cherelle’s life.”