President Donald Trump’s encounter with Russian President Vladimir Putin could be the catalyst for major diplomatic progress over Syria, one expert told CNBC Monday.

The first official dialogue between the two global leaders will take place in Helsinki’s presidential palace on Monday, marking a symbolic end to the Western effort to isolate Russia after its 2014 annexation of Crimea.

Ahead of the summit, neither side has sought to ramp up expectations of the meeting. And most external observers expect Trump and Putin to simply exchange warm words with one another, before potentially agreeing to a tentative deal to start talks on issues such as nuclear arms control and Syria.

“I think that along with bi-lateral arms control between Russia and the United States, Syria is quite likely today to be one of the top subjects,” Christopher Granville, Russia expert and managing director at TS Lombard, told CNBC’s “Squawk Box Europe” on Monday.

He explained that since Trump’s election, U.S. and Russian military forces have been working together “pretty closely” in the Syrian theater, marking a “complete change” to the previous Obama administration.

“So I think there is quite interesting scope for a significant breakthrough,” Granville added.

The war in Syria has changed dramatically over the last seven years, rapidly morphing into much more than a battle between those who are simply for and against Syrian President Bashar Assad.

Several countries and groups are involved — each with its own agenda while collectively making the situation extremely complex. Key supporters of Syria’s administration include Russia and Iran, while the U.S., Turkey and Saudi Arabia all back government rebels.

The United Nations estimates that almost 12 million Syrians have fled their homes since the outbreak of the civil war in March 2011, with the majority seeking refuge in neighboring countries or within Syria itself.

The pre-war population of Syria was roughly around 22 million people, meaning so far more than half of the country has been displaced.

Officials of the White House and the Kremlin have both sought to downplay expectations ahead of the summit, though Trump has said recently that “maybe some good” could come of the meeting.

“Unfortunately, no matter how well I do at the Summit, if I was given the great city of Moscow as retribution for all of the sins and evils committed by Russia over the years, I would return to criticism that it wasn’t good enough — that I should have gotten St Petersburg in addition,” Trump said via Twitter on Sunday.

The Helsinki summit constitutes the final destination of a nearly week-long European trip for Trump, during which he has frequently challenged traditional Western allies. The U.S. president has sown doubts about America’s commitment to the NATO alliance, reportedly threatened to kill off a future trade deal with the U.K. post-Brexit and described the EU as a “foe” of the world’s largest economy.

Meanwhile, for Putin, the fact that this summit is happening at all is seen as a geopolitical victory for Russia. That’s because talks between the U.S. and Russia could be viewed by Putin’s inner circle as evidence Washington is finally willing to recognize Moscow as a great power on the international stage.