According to Yarmish, this is not the first time Navalny has been poisoned.
Last year, while in a detention centre, he was reportedly victim of poisoning as well.
He was rushed to a hospital from prison where he was serving a sentence following an administrative arrest, with what his team said was suspected poisoning. Doctors then said he had a severe allergic attack and discharged him back to prison the following day.
"Obviously, now they've done the same thing to him again," she added.
The politician is in grave condition, Russia's state news agency Tass reported, citing the chief doctor at the hospital.
The Daily Beast reports that the latest poisoning happened just weeks after Navalny levelled corruption accusations against a Kremlin environmental inspector, Svetlana Radionova.
He cited documents tying Radionova to luxury real estate in both Moscow and Nice, saying "such wealth cannot be explained".
"It is so outrageous," Navalny said in a clip on YouTube, viewed by more than three million people.
- with AP