"We are awaiting the king's visit on Thursday," Ushakov said today, without elaborating.
The visit comes a month before members of the Opec oil cartel, of which Saudi Arabia is the biggest producer, are due to meet with the other nations that have joined them in cutting crude output, including Russia, to discuss extending the pact that has helped prop up prices.
Opec and its allies agreed from the beginning of 2017 to cut their production by around 1.8 million barrels per day for six months. It was subsequently extended through March 2018.
The pact has helped reduce the glut of crude supplies on the market and the price to climb to around $55 per barrel currently.
Moscow supports the regime of President Bashar al-Assad while Riyadh supports the opposition.
At least 3,000 people including 955 civilians were killed in September, the deadliest month of the conflict this year, the Syrian Observatory for Human Rights monitor said on Sunday.