Syrian mercenaries are arriving in Ukraine to fight for the Russians. This is in addition to the Kadyrovite Chechen forces that are already fighting there. Neither are like to be very Islamist (the Chechens may look it but not really), however it is worth pointing out that there are people in the Muslim world who would take the view that the territory of Ukraine (and large parts of Russia, for that matter) is properly Muslim territory. It was occupied for many centuries during the middle ages by the Golden Horde, an Islamic Mongol successor state.
The prompt for this was seeing a snippet of an Iraqi political commentator make pretty much exactly this argument (Ukraine should be part of the Caliphate) on a supposedly popular Iraqi politics show (looked a bit like newsnight).
If this really is a "big" historical event then, like all revolutions, wars etc that are worth their salt, we'll end up in a wildly different place than anyone intended at the outset. In this part of the world, it wouldn't be completely insane if an unexpected outcome might be some kind of religious conflict in the wider Pontic/Black Sea zone.