"His health has got worse and he's been receiving medical care at his home. No one has any idea of what will happen to him because there's very little that's known about the impact the nerve agent will have in the long run," the source told the Sunday Times.
Sergei Skripal and his daughter Yulia were found unconscious on a bench at a shopping centre in the UK city of Salisbury in March last year. Later, both Sergei and Yulia Skripal were discharged from the hospital where they were being treated.
Following their poisoning, the United Kingdom has accused Moscow of orchestrating the attack with what UK experts claimed was the A234 nerve agent. London has also announced that they suspect Russian nationals Alexander Petrov and Ruslan Boshirov of executing the poisoning, claiming they worked for Russia's GRU intelligence agency.
Moscow has refuted the allegations and repeatedly pointed to the lack of evidence provided by London. Petrov and Boshirov, in their turn, denied their involvement in the attack in an interview with the RT broadcaster. They said they indeed visited Salisbury in spring, but arrived there for tourist purposes, noting they work in the fitness industry.