The lawyer, Vladimir Zherebenkov, told ABC News on Thursday that he had seen Paul Whelan in Moscow's Lefortovo prison, where the former Marine has been held since he was arrested on espionage charges last week.
Paul Whelan, a 48-year-old corporate security director from the Detroit area, was arrested Friday on espionage charges.
While announcing the arrest three days later, the Russian Security Service said Whelan was caught "during an espionage operation", but gave no details.
The charge comes nearly a week after Whelan - a discharged Marine reservist - was detained in Moscow while on vacation in the country to attend the wedding of a fellow former US service member and a Russian woman, CNN reported.
The Marine Corps says the American detained in Russian Federation on espionage charges was convicted in a 2008 court-martial on charges related to larceny.
Earlier on Wednesday, Secretary of State Mike Pompeo said the United States will "demand his immediate return" if his detention is "not appropriate". We noticed that he was not in communication the 28th, which was very much out of character for him even when he was traveling. "I just don't see him putting himself in a position where he would be considered to break the law by a government like Russia's". Russian police detained Paul Whelan, who now faces espionage charges, almost a week ago.More news: Bangladesh goes to the polls under tight security
Whelan's current employer BorgWarner, an auto parts supply company, also released a statement on his arrest, saying, "We can confirm that Mr. Whelan now serves as the company's director, global security".
He was acting as a tour guide for other wedding guests who had not visited Russian Federation previously, his brother said.
It appears Whelan had been using a Russian social media platform similar to Facebook for the past 13 years. That was the same day, December 28, that Paul Whelan was detained. His brother says he was in Moscow to attend a wedding. His friends hadn't heard anything from Paul since 5 p.m. He received a "bad conduct" discharge from the Marines, according to his official military personnel file obtained by Fox News.
But it is looking increasingly like the Kremlin views Whelan more as a bargaining chip than anything else.
Secretary of State Pompeo was asked by reporters on Tuesday if he believed Russian Federation had taken Whelan in retaliation for Butina's detention.
In December, Russian national Maria Butina pleaded guilty in a Federal Court in Washington to acting as an illegal foreign agent. Prosecutors said she tried to build a back channel between Kremlin officials and Republican operatives during the 2016 presidential campaign.