Putin critic Navalny 'too ill to be moved' Mr Navalny has been in a coma since Thursday when he fell ill on a flight and his supporters called the doctors' decision "a direct threat to his life". They cited one report of "a deadly substance" dangerous not only to Mr Navalny but to all around him. Doctors treating him in Siberia said no poison had been found in his system. In a preliminary diagnosis on Friday, they said his condition might be the result of a "metabolic disorder" caused by low blood sugar. Mr Navalny is a prominent critic of Russian President Vladimir Putin. He made a name for himself by exposing official corruption and has served multiple jail terms. His team suspects a poisonous substance was put in his tea at an airport cafe in the city of Tomsk as he prepared to fly to Moscow. Activists in Germany have sent a plane to bring Mr Navalny to Berlin for treatment. The head doctor at the hospital treating Mr Navalny in Omsk in Siberia said the patient was too unstable to be transferred and that legal questions would need to be resolved before any move. ---------------- Alexei Navalny doctors refuse to let Putin critic leave Russia If confirmed as a poison attack, it would be the latest in a series of high-profile assaults, often with poison, against opposition figures and Russian dissidents that includes the 2018 poisoning of Sergei Skripal and the 2015 shooting death of the opposition politician Boris Nemtsov.