It's not clear to me what you are asking. A manifold is a set of points in [tex]R^n[/tex] and a function is not. A function may have a graph that is a manifold. For example, the graph of [tex]z= x^2+ y^2[/tex] is a parabola so 2 dimensional manifold in [tex]R^3[/tex]. On the other hand, a sphere is a manifold while [tex]x^2+ y^2+ z^2= r^2[/tex] is NOT a function.
Could you clarify- what definitions of "manifold" and "function" are you using?