I can't cough up any sources for this right now, but from what I know it is generally accepted that that the Slavs started migrating west in the 5th to 6th centuries. So during the time frame you are asking about the answer would be none, or at least a negligible amount.

But if you go forward a few centuries you will have the time when the Slavs migrated into the Eastern Roman Empire. At that time you see them starting to make a big impact on much of the Balkans (which in turn impacts the Easter Roman Empire). But I don't have enough knowledge to give you much more, so a professional will have to take the reins from here.