Hundreds of millions.
The African middle class numbers around 310 million, has doubled in the last twenty years, and is continuing to grow.
And do you honestly think they are paying or, they would pay in the future, SKY (or other broadcasters) fees in such numbers of hundreds of millions just to watch european football?
No idea. I answered the question you asked.
Take countries like Tunisia, Morocco or Egypt. There's a strong tradition about football there and millions of fans, but all the support is directed towards local teams and their stadiums are overcrowded of fans but to pay for watching a foreign team is still a luxury thing.
A luxury that growing middle classes might pay for, for instance?
In fact becoming fan of something or someone that has nothing to do with your country is not really easy.
I don't know about Africa, but as someone who works with rural (and poor!) communities in the Middle East, this is not at all my experience. Though I suppose what 'has nothing to do with your country' is not straightforward to define.
China tried to invest in local football and failed. As a proof of that all the top players are leaving the country, if they haven't left already, and they'll not be replaced by other players with high salaries as the clubs' owners aknowledged the costs didn't worth the investment. Chinese people still prefer individual sports, that's a cultural thing.
And yet their football audiences are growing.