Russian opposition leader Alexei Navalny has been moved from hospital and back to jail on Monday, despite his doctor raising suspicions about a possible poisoning.
Anastasiya Vasilyeva, who has been Mr Navalny’s physician for several years, said that the "allergic reaction" he suffered from could be consistent with chemical poisoning.
The 43-year-old was rushed to hospital on Sunday after experiencing swelling and a rash - something he had never before.
The source of the "allergic reaction" was unclear.
Mr Navalny is currently serving a 30-day prison sentence after calling for an unsanctioned protest.
He was arrested several days after a major opposition rally that ended with nearly 1,400 people being detained last week.
Access to Mr Navalny is restricted and Dr Vasilyeva said that hospital officials who previously diagnosed him with an allergic reaction refused to run the necessary tests on him.
Dr Vasilyeva said she would visit Mr Navalny again, later on Monday.
On Saturday, baton-wielding police wrestled with protesters in arguably the largest unsanctioned protest in Russia in a decade.
Nearly 1,400 people were arrested at the anti-government protests in what the Kremlin called a legitimate response to unauthorised rallies.
Opposition activists as well as ordinary Muscovites took to the streets to vent their anger over officials' decision to exclude a dozen independent candidates from the ballot for the upcoming vote for the Moscow city legislature.
Amongst those arrested were several would-be candidates, two of who, Ilya Yashin and Dmitry Gudkov, face a court hearing later Monday.
At least 21 people including Mr Navalny's supporters and journalists were briefly detained outside the hospital late on Sunday.
His ally Leonid Volkov has complained about unsanitary conditions at the detention facility where he had also been held before.
Mr Navalny has been the Kremlin's most formidable foe since 2011 when he led a massive wave of protests against President Vladimir Putin and his party.
He has since been convicted on two sets of criminal charges, largely regarded as politically motivated, and spent numerous stints in jail for disturbing public order and leading unsanctioned protests.