The Prosecutor General's Office said that since Moscow considers Wolodymyr Satsiuk, or Vladimir Satsyuk, to be a Russian citizen, he cannot be extradited.
Satsiuk is also facing abuse of office and forgery charges in Ukraine, which requested his extradition in April 2008.
Ukraine has been negotiating with Russia over the extradition of three people who it says may have been involved in the Yushchenko poisoning, but the Russian Prosecutor General's Office said it had received no other extradition requests.
Yushchenko became seriously ill in early September 2004, the day after attending a reception and dinner with Ukrainian security services leaders.
He suffered from a series of symptoms, including back pain, acute pancreatitis and nerve paralysis on the left side of his face. After the illness, his face became heavily disfigured - grossly jaundiced, bloated and pockmarked.
Many have linked Yushchenko's poisoning to a group of senior Ukrainian officials, including the former head of the Security Service of Ukraine (SBU), Ihor Smeshko, and his deputy, Satsiuk.
All of them are believed to have fled to Russia and received Russian citizenship.
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Russia has become very adept in playing the diplomatic game, in which victory depends on choosing the right associate or partner. But there are a growing number of claimants to this role in the new horizontal and interdependent world. Aside Syria and Iran, being still important, the new venues for the application of practical diplomacy may well be Ukraine, the East China Sea and Afghanistan.