  We analyze the influence of an impurity in the movement of discrete breathers
in Klein--Gordon chains. We observe that the moving breather can cross the
impurity, can be reflected by it, or can be trapped originating a
quasi-periodic breather. We find that resonance with a nonlinear localised mode
centred in the impurity is a necessary condition in order to observe the
trapping phenomenon, as a difference with the resonance condition with a linear
localised mode when this problem is studied within the Nonlinear
Schr\"{o}dinger Equation approximation.
