Scalar fields in curved backgrounds are assumed to be composite objects. As an example realizing such a possibility we consider a model of the massless tensor field l_μν(x) in a 4-dim. background g_μν(x) with spontaneously broken Weyl and scale symmetries. It is shown that the potential of l_μν, represented by a scalar quartic polynomial, has the degenerate extremal described by the composite Nambu–Goldstone scalar boson ϕ(x):=g^μνl_μν. Removal of the degeneracy shows that ϕ acquires a non-zero vev ⟨ϕ⟩0=μ which, together with the free parameters of the potential, defines the cosmological constant. The latter is zero for a certain choice of the parameters.