The presidents of Turkey, Iran and Russia will meet in Ankara on Monday as part of the Astana process, with the three countries holding regular meetings in an attempt to resolve the Syrian conflict, reports the Voice of America.
The fate of the last rebel stronghold in Idlib is expected to be the main topic.
As Syrian government forces advance on Idlib, Ankara warns of a looming humanitarian catastrophe.
In recent weeks, Syrian regime forces have been mercilessly attacking rebel positions in Idlib.
Many of the residents of the enclave, which has a population of about 3 million people, are fleeing towards the Turkish border.
Preventing the humanitarian crisis is expected to be a priority for Turkish President Recep Tayyip Erdogan during a meeting with his Iranian and Russian counterparts.
"The situation is critical," said Professor Mesut Casin of Yeditepe University. "This situation continues and it is unacceptable. Why? Because the winter is coming."
About 4 million Syrian refugees already live in Turkey, and Erdogan warns that the country cannot accept more.
Discontent among the Turkish public is growing, and the authorities have begun to crack on illegal refugees.
During the summit, Erdogan is expected to try to get the support of Russian President Vladimir Putin to prevent a mass exodus from Idlib.
While Russia and Turkey support opposing sides in the Syrian conflict, the two leaders are cooperating on the Syrian issue as part of a larger rapprochement between the countries.
"The Astana summit in Ankara will only delay what should happen in Idlib," said Aydin Selcen, a former senior Turkish diplomat. "Idlib will become part of the Syrian state and the regime of Bashar al-Assad."
" The Syrian army does not have enough power to drive the Turkish army out of Syria. But Syria is supported by Russia. The final phase is approaching. All parties, including Russia and the United States, want to move on to the next step: writing a new constitution," he added.
Meanwhile, Turkey is strengthening its military presence in Idlib. This raises the threat of a clash between Turkish and Syrian forces.
"There is a new threat that Turkey and Syria will start fighting with each other, and then the third guarantor country, Russia, will be responsible for the situation. I hope Putin is a smart man and does not want to lose Turkey. This would be the collapse of Turkish-Russian relations," Professor Mesut Casin warned.
Critics of the Astana process note that it has yielded only few concrete results. However, given the looming crises in Idlib, the consequences of inaction at the upcoming summit could be significant.