  It is shown that the causal structure associated to string-like solutions of
the Fadeev-Niemi (FN) model is described by an effective metric. Remarkably,
the surfaces characterising the causal replacement depend on the energy
momentum tensor of the background soliton and carry implicitly a topological
invariant $\pi_{3}(\mathbb{S}^2)$. As a consequence, it follows that the pre-
image curves in $\mathbb{R}^3$ nontrivialy define directions where the cones
remain unchanged. It turns out that these results may be of importance in
understanding time dependent solutions (collisions/scatterings) numerically or
analytically.
