"Her being afraid of not being released is mostly connected to the negotiations, which we are not aware of at all," Griner's attorney Alexandr Boikov told ABC News on Thursday.
After being detained in Russia for more than five months, Griner was found guilty on drug charges in a Moscow-area court on Aug. 4 and was sentenced to nine years in prison.
Her attorneys filed an appeal on Aug. 15 and a hearing is scheduled for Oct. 25.
"She is not very much hopeful for the appeal because the first court decision -- the verdict showed that the case is totally unjust even by present Russian standards, and we are not hoping for a big release, but of course we hope for the best," Boikov told ABC News.
According to Boikov, decisions on appeals are usually made during one hearing, but other hearings could be scheduled and he expects a decision by the end of October.
Griner, a 31-year-old Houston native who plays professional basketball for the Phoenix Mercury, was detained on Feb. 17 at Sheremetyevo International Airport in Khimki as she returned to Russia to play during the WNBA's off-season after she was accused of having vape cartridges containing hashish oil, which is illegal in the country.
Griner pleaded guilty to drug charges in July, saying that the vape cartridges containing hashish oil were in her luggage mistakenly and that she had no "intention" of breaking Russian law.
Since she was detained in February, Griner has only spoken to her wife, Cherelle Griner, twice and currently "she's not having phone calls with her family," Boikov said.
He added that while requests are not being "denied," there's "a lot of bureaucracy and paperwork and back and forth between different institutions" so scheduling phone calls has been "very hard."
Boikov said that Griner is also experiencing some physical "pain" in prison, where she is unable to exercise or receive physical therapy.
"She has some issues with her knees, with her back, I think basketball-related but of course, she doesn't have a big bed, a good mattress or a time or place to exercise and to keep her muscles in shape," he said.
"Of course, without movement and the conditions in jail, she is not in very good shape," he added.
The U.S. government classified Griner's case on May 3 as "wrongfully detained," meaning the U.S. will more aggressively work to negotiate her release even as the legal case against her plays out, the State Department has said.
Russia's invasion of neighboring Ukraine began one week after Griner was detained, and some officials have expressed concern that Americans jailed in Russia could be used as leverage in the ongoing war.
President Joe Biden initially told CNN on Tuesday that he would be open to meeting with Russian President Vladimir Putin at the G-20 November summit to discuss Griner's release, but when asked by ABC News on Wednesday about a potential meeting, the president said, "not with Putin."
White House press secretary Karine Jean-Pierre told reporters on Wednesday that Biden "has no intention of meeting with President Putin."
State Department spokesperson Ned Price told ABC News on Wednesday that "securing the release of Paul Whelan and Brittney Griner is a priority for this administration."
Asked about Griner's condition and whether the U.S. has access to her in prison, Price said that the "most recent consular access with Brittney Griner was at the beginning of August."
"We continue to impart on the Russian government the necessity of consistency and regular consular access to Brittney Griner but also to all of those Americans who are detained in Russia," he added.
ABC News' Tanya Stukalova, Shannon Crawford and Ben Gittleson contributed to this report.