"No. The only issue on the agenda is forming a joint delegation of opposition," the source said when asked whether a constitutional change will be discussed.
Lavrov is going to meet with 25 representatives of opposition factions on Friday. Members of the National Coordination Body for Democratic Change, Cairo group, Moscow group, Hmeimim group, the Movement of the Pluralistic Society and PYD are among them, according to the source.
General Coordinator of Saudi-backed High Negotiations Committee (HNC) Riyad Hijab also was invited, but has not confirmed his participation yet, the source added.
During the previous rounds of Geneva talks, the HNC insisted on its exclusive right to represent the Syrian opposition and ruled out the possibility of joining efforts with other factions.
Next round of Geneva talks is expected on February 8.