Chechen leader Ramzan Kadyrov has been taken to hospital with suspected coronavirus, Russian media report.
He was flown to Moscow on Wednesday for treatment after developing flu-like symptoms, said Interfax news agency quoting a source, BBC reported.
The authoritarian leader - who previously fought against Moscow as a Chechen nationalist - is now a key ally of Russian President Vladimir Putin.
Mr Kadyrov has come under scrutiny for imposing his own interpretation of Islamic law in the region, as well as for his poor human rights record.
Unconfirmed reports suggested a plane belonging to the 43-year-old leader was tracked flying from near the Chechen capital, Grozny, to Vnukovo airport in Moscow on Thursday afternoon.