Kasyanov, 51, the leader of the People's Democratic Union, said the mass protests will begin "when people in Russia realize that they are in a deep economic hole."
"In less than half a year, when the current leadership has spent all the money, there will be nothing left in the arsenal to engage with the public except batons and the use of force," Kasyanov told a roundtable on relations between the EU and Russia in Tallinn.
Russia has been hard hit by the global financial crunch that was sparked by the subprime mortgage crisis in the United States last summer and quickly spread to the rest of the world.
Russian authorities have pledged however that the anti-crisis measures currently undertaken by the government will not affect social expenditures and state support to Russians.
Kasyanov, who was prime minister during Vladimir Putin's first term as president in 2000-2004, said the country's economy could be saved by expanding political rights and freedoms in Russian society.
He also noted that the country's foreign policy has become tougher.
"The freedom space has become more squeezed and the gap in values between Russia and the West has deepened," he said.
Kasyanov has accused the Russian authorities of "pressure and intimidation" after he was banned from running in the March 2008 presidential elections over irregularities in his application. The election commission ruled his supporters had collected forged signatures to support his bid.
A former member of The Other Russia opposition coalition, Kasyanov was accused in 2005 of putting up for sale in 2003 two houses formerly owned by the government. In 2007, the court ordered him to return the property and pay the government in damages.
