To the extent that one can find elements of Victorian poetry in the eighteenth century, or of Modernism in the Romantic poets, I suppose one can always find elements of post-modernism in a major Modernist poet. As the Marxists used to say, in any cultural phenomenon there is a residual dimension, a dominant or hegemonic one, and emergent elements. Of course if T.S. Eliot were "hegemonically" post-Modern, we wouln't be calling him a Modernist, but a post-Modernist, but it's only natural that elements of contemporary poetry, if that's what postmodernism means here, are to be found in a major forerunner—above all with the benefit of hindsight, you know, the "T.S. Eliot's-influence-on-Shakespeare" kind of thing that David Lodge wrote about.
(From a ResearchGate discussion: "Can we find postmodern elements in T. S. Eliot's poetry?")