It has been claimed by eyewitnesses that there was a large explosion in Huraytan, northern Syria, while three fighter planes were seen overhead.
Rumours of a jet being shot out of the sky come amid heightening tensions between Russian president Vladimir Putin and the West.
However, Russia has claimed its forces hit 55 ISIS targets in Syria in the 24 hours to Saturday - although Russian's jets were also a key factor in helping Syrian troops massive ground offensive.
The Russians - who have announced plans to increase the number of strikes against ISIS targets - have also clashed with Turkey, after claims that one of their bombers violated Turkish airspace.
It has been claimed by eyewitnesses that there was a large explosion in Huraytan, northern Syria, not far from the Turkish border, while three fighter planes were seen overhead
But neither side has yet said whether rumours of another of Russia's planes was shot down in a separate confrontation.
According to the Daily Express, one journalist tweeted that three Turkish planes had been responding to 'mysterious' lock-ons from MIG-29 jets, which are used by Russian forces.
Meanwhile, a spokesman for Nato said it had so far received no reports of a plane being shot down
Yesterday it emerged ISIS had taken advantage and launched a new offensive in Aleppo province following Russia's decision to target Free Syrian army rebels and Al-Qaeda affiliated groups.