Russia's envoy for Middle East affairs has said that rebel forces are gaining ground against the Syrian government and could win the battle against President Bashar al-Assad.
The announcement by Deputy Foreign Minister Mikhail Bogdanov comes as a top NATO official also said on Thursday that he believed Assad's regime was nearing "collapse".
Bogdanov said on Thursday that Russia was working on plans to evacuate its citizens from Syria if necessary.
"One must look the facts in the face," the state-run Russian news agency RIA quoted Bogdanov as saying.
"The regime and government in Syria is losing control of more and more.
"Unfortunately, a victory of the Syrian opposition cannot be ruled out."
His remarks were the clearest sign yet that Moscow is preparing for the possible defeat of Assad's government in a conflict that has left more than 40,000 people dead since March 2011, according to activists.
Russia has helped shield Assad's government from UN Security Council censure and sanctions, resisting Western pressure to join efforts to push him from power.
The secretary-general of NATO said on Thursday that he thought the Syrian government was nearing collapse, and condemned the alleged use by Assad's forces of Scud missiles to attack rebels.
"I think the regime in Damascus is approaching collapse," Anders Fogh Rasmussen told reporters after a meeting with Dutch Prime Minister Mark Rutte at the military alliance's headquarters in Brussels.
"I think now it is only a question of time."
Rasmussen said the reported use of Scud missiles by the Syrian government showed "utter disregard" for the lives of Syrian people.
Syria's foreign ministry denied on Thursday using Scud missiles against rebels.
Offer to Assad
Meanwhile, the new leader of Syria's opposition told the Reuters news agency that the Syrian people no longer need the intervention of international forces to topple Assad, as rebels push towards the heart of Damascus.
Mouaz al-Khatib, the scion of a Damascene Muslim religious dynasty, said the opposition would consider proposals from Assad to surrender power and leave the country, but would not give any assurances until it saw a firm proposal.
Khatib was speaking on Wednesday night after a meeting of Western and Arab nations with the Syrian opposition in the Morocca.
During the "Friends of Syria" meeting in the city of Marrakech, more than 100 states officially recognised Syria's new opposition coalition as the "legitimate representative" of the country, opening the way for greater assistance.
"The horrific conditions which the Syrian people endured prompted them to call on the international community for military intervention at various times," Khatib said.
"Now the Syrian people have nothing to lose. They handled their problems by themselves. They no longer need international forces to protect them."
Referring to Assad, he said: "I only hope that he knows that he has no role in Syria or in the lives of the Syrian people. The best thing is that he steps down and stops drinking the blood of the Syrian people."