Artiomas Us, who was arrested at Milan Malpensa Airport on October 17, pledged not to leave his residence near Milan and was required to wear an electronic bracelet.
U.S. officials accuse A.Usa, the son of the governor of Siberia, of illegally selling U.S. technology to Russian arms companies.
An Italian court agreed to extradite him to the United States on Tuesday, but the man disappeared the next day, media reported.
According to La Repubblica newspaper, police checked on A.Usa early on Wednesday morning, but around lunchtime his electronic bracelet sent off an alarm and he has not been seen since.
Several Italian newspapers speculated that he may already be abroad.
On Friday, his father Alexander Us, the governor of the Krasnoyarsk region of Siberia, expressed concern.
“As a father, I am very worried about my son,” he said at the press conference. “I don’t know where he is and I don’t know what happened.”
“I can only say that, according to Artyom, the apartment where he lived was well guarded by the police. They even checked on him several times a night. So I don’t really understand how he disappeared,” he added.
He had previously condemned his son’s arrest as political and repeated it on Friday, saying his son was involved in a geopolitical game and saying the case against him was fabricated.
Artyom Us was one of five Russians arrested at Washington’s request for illegal schemes to export powerful US military technology to Russia.
The US Department of Justice said some of them “were found on battlefields in Ukraine”.
After his arrest in Italy, Russia placed Artyom Us on its wanted list, and media reported that he was accused of money laundering, and that Moscow could seek his extradition.