"We have every reason to believe this could be a question of the deliberate, forcible detention of a Russian citizen or possibly their coercion into a staged announcement," foreign ministry spokeswoman Maria Zakharova said.
Yulia Skripal was discharged from hospital on Monday, more than a month after the March 4 nerve agent attack in the English town of Salisbury which has sparked a global diplomatic crisis.
While her whereabouts are unknown, Skripal said she is being supported by police officers who are keeping her informed of their high-profile investigation.
On Wednesday, she said she did not currently wish to take up an offer of consular assistance from the Russian embassy, according to a note released by London's Metropolitan Police.
London blames Moscow for the attack, an accusation vehemently denied by the Russian government which has requested access to the Skripals as Russian citizens.
Sergei Skripal's niece, Viktoria Skripal, has spoken to Russian media about the poisoning and last week saw her application to visit the UK rejected, with officials saying it did not comply with immigration rules.
Yulia Skripal on Wednesday cast doubt on her cousin's account, saying: "Her opinions and assertions are not mine and they are not my father's."