Pussy Riot's Nadezhda Tolokonnikova, 23, who is serving a two-year sentence for her part in the feminist punk group's anti-Putin protest at a Moscow cathedral last year has been taken to a prison hospital.
Pyotr Verzilov,her husband, spoke to Sky News saying she was suffering from headaches and was in the process of undergoing tests to determine if her existing medical conditions were to be sited as potential catalysts.
"The medical centre is checking whether the previous sicknesses and diagnoses that Nadezhda has pose some sort of danger to her health while she lives through the daily life of the prison regime," he explained.
"Everything is based around eight-hour working shifts and it's not clear whether, for example, her headaches that she has are influenced by these long shifts."
Mr Verzilov said she was required to sew police, military and various other types of special forces clothes, but that she was determined to keep her spirits up.
"She is a brave girl and gets her spirits together and she is in quite a good mood," he said.
A spokeswoman for the Federal Prison Service confirmed that Mrs Tolokonnikova had been moved to a prison hospital in the Mordovia province of western Russia, where she is being held at Corrective Colony No 14.
In an interview published in the independent Novaya Gazeta newspaper last week, Mrs Tolokonnikova described her daily prison life.
Her fingers had been punctured by the sewing machine needle but she has now gathered her speed and can maintain a quota of lining for 320 jackets per day. As is the norm, she bathes once a week and uses cold water to wash the rest of the week.
Mrs Tolokonnikova said she meditates to prevent her spirit from being dulled by the monotonous labour, adding that the main thing she misses at her prison colony is the ability to read freely.
Pussy Riot staged its punk prayer protest at Moscow’s Christ the Saviour Cathedral on February 21, 2012, appealing to the Virgin Mary to “throw Putin out”.
Three of its members were convicted of hooliganism motivated by religious hatred and sent to prison, although one, Yekaterina Samutsevich, was later freed on appeal.