The American basketball star Brittney Griner appeared in a Russian court on Wednesday, in a case that has turned her into an unlikely pawn in a diplomatic tussle between Russia and the United States as the war in Ukraine has created the deepest rift between the two superpowers since the end of the Cold War.

Washington continues to send weapons to the Ukrainian military and has imposed sweeping sanctions on Russia, and even the decades-long partnership in outer space appear to be ending as Moscow announced that it would leave the International Space Station after its current commitment expires at the end of 2024.

The Russian authorities detained Ms. Griner, 31, a two-time Olympic gold medalist who plays for the Phoenix Mercury, about a week before President Vladimir V. Putin’s forces invaded Ukraine in February. Russia accused her of having two vape cartridges of hashish oil in her luggage when she arrived at an airport near Moscow. Russia did not make her detention public until after the invasion began.

Ms. Griner had been traveling to Russia to play with a team in Yekaterinburg, about 900 miles east of Moscow, during the W.N.B.A. off-season. She was charged with willfully smuggling the vape cartridges, violating Russian laws prohibiting the importation of narcotics.

She now faces a possible 10-year sentence.

Ms. Griner pleaded guilty this month, saying that she had made a mistake and unintentionally carried a banned substance into Russia because she had packed in a hurry. In the Russian justice system, trials go on even when defendants plead guilty. Ms. Griner’s lawyers have said they hope her plea would make the court more lenient.

On Wednesday, her defense team continued to present evidence that she had not intended to break the law.

They have argued that she did not intend to smuggle drugs into Russia and that, like many other international athletes, she had used cannabis to help ease pain from injuries. They also presented a medical note from Ms. Griner’s doctor recommending cannabis to help ease chronic pain.

With her guilty plea making the verdict seem a foregone conclusion, experts say that her best hope is that the Biden administration finds a way to swap her for a high-profile Russian who is being held by the United States. Yet the administration is reluctant to create any incentive for the arrest or abduction of Americans abroad.