[en] Accumulated γ-ray evidence on the time variability of the pulse height ratio (PHR) of the Crab pulsar is shown to be compatible with a long-term (∼ 10.7 y) periodicity and can be interpreted as the free precession of the underlying neutron star. A prediction for the value of PHR by the coming GRO-EGRET γ-ray observations under the present model is presented