Russia's government will not have the capacity to help all the state-run companies under sanctions because of its commitment to large state spending projects, the former finance minister said.
Alexei Kudrin has been a persistent critic of the government's handling of the standoff with the West over Ukraine.
Kudrin told delegates at a foreign business conference that he expected the Russian economy to stagnate or weaken this year, while he predicted negative growth in 2015.
A number of Russian companies, including the oil giant Rosneft, have suggested they would seek state assistance after having their access to Western financial markets cut off by European and US sanctions. The state-run oil producer has asked the government for $40bn.
In the current climate, with the economy stalling and spending on social projects rising, Kudrin said the government will struggle to fill the financial gap.
"Companies turn to the government, but the government's support is limited, bound by continued large social spending," Kudrin said.
As long as the fighting continued in eastern Ukraine, Russia would face a harsh investment climate, Kudrin added.
The United States and the European Union imposed their latest round of sanctions on Russia on September 12. The measures included restricting some of Russia's top energy companies' access to financial markets in the West, as well as travel bans and asset freezes on individuals.
While a ceasefire has been declared in eastern Ukraine, Western have said the latest sanctions would be lifted if Russia removed all its forces from its neighbour's territory.
More than 3,000 people have been killed since fighting erupted in eastern Ukraine in mid-April.