Given a finite field Fq of q elements, we consider a trajectory of the map u → f (u) associated with a polynomial f ∈ Fq[X]. Using bounds of character sums, under some mild condition on f , we show that for an appropriate constant C > 0 no N Cq 1/2 distinct consecutive elements of such a trajectory are contained in a small subgroup G of F * q , improving the trivial lower bound #G N . Using a different technique, we also obtain a similar result for very small values of N . These results are multiplicative analogues of several recently obtained bounds on the length of intervals containing N distinct consecutive elements of such a trajectory.