"If there is any request then it would naturally be discussed and evaluated through bilateral contacts and dialogue," Kremlin spokesman Dmitry Peskov was quoted as saying by Russian news agency RIA Novosti.
"But it is difficult to talk about this hypothetically."
The United States says that Russia -- one of Assad's last remaining allies -- has covertly deployed troops, artillery units and tanks to Syria.
Moscow says it is sending arms to Syria under existing contracts but denies bolstering its forces in the country.
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US officials have expressed fears Russia may strike Western-backed rebel groups battling Assad and ultimately risk a confrontation with forces fighting the Islamic State (IS) group.
Moscow has been pushing for a broader coalition of forces to take on IS, but key Western and regional players have ruled out fighting alongside Assad.
Russian news website Gazeta.Ru reported on Friday that some Russian soldiers were disputing possible orders to be sent to Syria.
Presidential spokesman Dmitry Peskov said that the Kremlin has no knowledge of complaints by soldiers to its human rights council.