  Tibet-AS$\gamma$ collaboration has recently reported a measurement of diffuse
$\gamma$-ray flux from the outer Galactic disk in the energy range reaching
PeV. We complement this measurement with the Fermi/LAT measurement of the
diffuse flux from the same sky region and study the pion decay model of the
combined Fermi/LAT+Tibet-AS$\gamma$ spectrum. We find that within such a model
the average cosmic ray spectrum in the outer Galactic disk has the same
characteristic features as the local cosmic ray spectrum. In particular, it
experiences a hardening at several hundred GV rigidity and a knee feature in
the PV rigidity range. The slope of the average cosmic ray spectrum above the
break is close to the locally observed slope of the helium spectrum
$\gamma\simeq 2.5$, but is harder than the slope of the local proton spectrum
in the same rigidity range. Although the combination of Fermi/LAT and
Tibet-AS$\gamma$ data points to the presence of the knee in the average cosmic
ray spectrum, the quality of the data is not yet sufficient for the study of
knee shape and cosmic ray composition.
