  We extend Derrick's theorem to the case of a generic irrotational curved
spacetime adopting a strategy similar to the original proof. We show that a
static relativistic star made of real scalar fields is never possible
regardless of the geometrical properties of the (static) spacetimes. The
generalised theorem offers a tool that can be used to check the stability of
localised solutions of a number of types of scalar fields models as well as of
compact objects of theories of gravity with a non-minimally coupled scalar
degree of freedom.
