The 44-year-old Navalny has led an anti-corruption crusade against the Kremlin, exposing government officials, including some at the highest level, of using their authority for personal gain.
In a 2017 interview with CBS News, Navalny said he was uncertain whether his campaign against political corruption could see him jailed.
"Mr. Putin personally decides such things, and no one understands what is in his head," Navalny said.
When asked what the chances were that he’d end up dead, Navalny answered: "Well, like, 50% I would be killed, or I would not be killed.”
Navalny was placed on a ventilator in a hospital intensive care unit in Siberia after falling ill from suspected poisoning during a flight, his spokeswoman said Thursday. (AP Photo/Pavel Golovkin, File)
Navalny was on a ventilator in a hospital intensive care unit on Thursday. He felt sick on a flight returning to Moscow from Tomsk, a city in Siberia, and made an emergency landing in Omsk, Navalny's spokeswoman Kira Yarmysh said on Twitter. His allies have said they believe the suspected poisoning is linked to his political activity.
Navalny is not the first opposition figure to suffer from a mysterious poisoning.
In 2018, Pyotr Verzilov, affiliated with Russia's protest group Pussy Riot, ended up in an intensive care unit after a suspected poisoning and had to be flown to Berlin for treatment. Opposition activist Vladimir Kara-Murza was hospitalized with poisoning symptoms twice — in 2015 and 2017. Both said they believed they were poisoned for their political activity.
Like many other opposition politicians in Russia, Navalny has been frequently detained by law enforcement and harassed by pro-Kremlin groups. In 2017, he was attacked by several men who threw antiseptic in his face, damaging one eye.
In 2018, Navalny tried to challenge Putin in the presidential election but was ultimately banned from running.
Last month, Navalny had to shut down his Foundation for Fighting Corruption after a financially devastating lawsuit from Yevgeny Prigozhin, a businessman with close ties to the Kremlin.
Doctors at the Omsk ambulance hospital №1 said a variety of diagnoses are being considered but refused to give details. Anatoliy Kalinichenko, the deputy chief doctor of the hospital, told reporters that Navalny was in grave yet stable condition.
The Associated Press contributed to this report.