Russian Presidential Administration Chief of Staff Sergei Ivanov made the comments during a speech at the International Institute for Strategic Studies' Global Strategic Review conference in Stockholm, RIA Novosti reported.
"I am talking theoretically and hypothetically here, but if we see any certainty that Assad is cheating, we could change our position," Ivanov said.
The Obama administration has said there is conclusive evidence the Assad regime used chemical weapons in an Aug. 21 attack in which more than 1,400 people were killed. Russia has said evidence shows rebels used chemical weapons.
A hypothetical situation in which Russia would change its position on Syria is if both the regime and the rebels used chemical weapons, Ivanov said.
"I can imagine what the global community will do then," Ivanov said, adding that should that scenario arise, Russia would take "only diplomatic action -- what else can we do?"
Russia has supported Assad's regime and has opposed an international military intervention, since the start of Syria's civil war in March 2011.