Preparations for the latest efforts to end Syria's five-year-old civil war have been plagued by complications, including a dispute over who should represent the opposition.
United Nations special envoy to Syria Staffan de Mistura on Tuesday sent out invitations to the talks, which are due to begin in Geneva on Jan 29, without revealing who would take part.
There was no mention of al-Mualem's role in the negotiations on Syrian state media, Reuters reported.
"An invitation from de Mistura was sent to Walid al-Mualem as head of the government delegation," Gatilov was quoted as saying by Interfax news agency.
Russia has close ties with the Syrian government and opposes calls from the United States and Western powers for its regional ally, President Bashar al-Assad, to step down.
Al-Mualem last met Russian Foreign Minister Sergei Lavrov in Moscow in November to discuss efforts to end the war.