Russia is already putting their foot down and Syrian forces have crossed the Euphrates in some spots per twitter. I would imagine the Turkish offensive goes as far as the Russians are willing to allow at this point given that Assad's forces are already pushing north.
Russia has said it will not allow clashes between Turkish and Syrian forces, as Turkey's military offensive in northern Syria continues.
"This would simply be unacceptable... and therefore we will not allow it, of course," said Moscow's special envoy for Syria, Alexander Lavrentyev.
The withdrawal of US troops from the region, announced last week, gave Turkey a "green light", critics say.
Russia is a key military ally of Syrian leader Bashar al-Assad.
Mr Lavrentyev, during a visit to the United Arab Emirates, described Turkey's offensive as "unacceptable".
https://www.bbc.com/news/world-middle-east-50058859?ocid=socialflow_twitter