The rate of the linear collisionless damping (Landau damping) in a classical electron gas confined inside a heated ionized spherical cluster is calculated. The general formula is obtained which expresses the decrement of the damping via parameters of a single-particle selfconsistent potential for electrons. The value of this decrement versus the electron temperature is calculated in two margin cases of mirror and diffuse reflection of electrons from the boundary of a selfconsistent potential.