I would risk and start him
For normal players, being at this stage of the competition is a one of a kind experience. We all know it is very likely this will be not his first and last CL semis...but no one knows what can happen in life and maybe there will be not second chances.
SUperb players like Ibra have won few in europe even when being uberly talented. You dont know what will happen.
SO he better takes his chance now. If he goes wrong...well it will be sub time. Obs he will be cold as hell....but who knows...Pirlo came was thrown into the fray days after he resumed training....so maybe pogba can do it too.