Kremlin critic Alexei Navalny is due back in Moscow later on Sunday for the first time since he was nearly killed last year by a nerve agent attack.
He says the authorities were behind the attempt on his life, an allegation backed up by investigative journalists but denied by the Russian government.
Mr Navalny, 44, faces arrest on his return from Germany, where he has been receiving medical treatment.
But he has appealed to supporters to meet him off the flight.
A “Let’s meet Navalny” page has been set up on Facebook (in Russian), with thousands of people saying they will go or expressing an interest, despite forecasts of extreme cold.
He has said he is almost fully recovered from the attack, that he misses Moscow and there was never any doubt that he would return.
The Russian opposition figure collapsed on an internal flight in Siberia last August and it later emerged he had been poisoned with a Novichok nerve agent.
Russian authorities have consistently denied any role in the poisoning, and the Kremlin has rejected Mr Navalny’s claims that President Vladimir Putin himself ordered it.
The Russian authorities have warned Mr Navalny could face imprisonment after missing a prison service deadline in December to report at an office in Moscow.
The prison service accuses him of violating conditions imposed after a conviction for embezzlement, for which he received a suspended sentence. He has always condemned the case as politically motivated.
Separately, Russia’s investigative committee has launched a new criminal case against him on fraud charges related to transfers of money to various NGOs, including his Anti-Corruption Foundation.
Mr Navalny has asserted that Mr Putin is doing all he can to stop his opponent from coming back by fabricating new cases against him.