Lawyers for American basketball star Brittney Griner have filed an appeal against her nine-year prison sentence for drug possession.

Griner, a centre for the Phoenix Mercury who had been playing in Yekaterinburg during the WNBA off-season, was arrested in February at Moscow’s Sheremetyevo airport after vape canisters containing cannabis oil were found in her luggage. She was convicted on 4 August.

Lawyer Maria Blagovolina said on Monday the appeal had been filed, but declined to give details. Alexander Boykov, a lawyer at Moscow Legal Centre who represented Griner in court, told Reuters the appeal would be mainly based on alleged violations in the course of the investigation.

Griner’s defence team argued in court that some of her case files had been drawn up without being translated for her into English. It was not clear how soon an appeal could be heard.

A formal appeal may indicate that no political deal has been reached for a prisoner swap involving Griner between Russia and the US. Russian officials have said that they would consider an exchange but only after Griner’s appeal process had been exhausted and her sentence came into effect.

Blagovolina and Boykov said after the conviction that the sentence was excessive and that in similar cases defendants have received an average sentence of about five years, with about a third of them granted parole.

Griner admitted that she had the cannabis oil canisters in her luggage, but said she had inadvertently packed them in haste and that she had no criminal intent. Her defence team presented written statements that she had been prescribed cannabis to treat pain.

Before her conviction, the US state department declared Griner to be wrongfully detained.

The US secretary of state, Antony Blinken, took the unusual step of revealing publicly in July that the US had made a “substantial proposal” to get Griner home, along with Paul Whelan, an American serving a 16-year sentence in Russia for espionage. He did not elaborate, but the AP and other news organisations have reported that the US has offered to free Viktor Bout, a Russian arms dealer who is serving a 25-year sentence in the US and once earned the nickname the “Merchant of Death”.

On Sunday, a senior Russian diplomat said exchange talks had been conducted.

“This quite sensitive issue of the swap of convicted Russian and US citizens is being discussed through the channels defined by our presidents. These individuals are, indeed, being discussed. The Russian side has long been seeking the release of Viktor Bout. The details should be left to professionals, proceeding from the ‘do not harm’ principle,’” Alexander Darchiev, head of the foreign ministry’s North America department, told state news agency Tass.

• With Reuters