  We study anomalous chiral symmetry breaking in two-flavour QCD induced by
gravitational and QCD-instantons within asymptotically safe gravity within the
functional renormalisation group approach. Similarly to QCD-instantons,
gravitational ones, associated to a K3-surface connected by a wormhole-like
throat in flat spacetime, generate contributions to the 't~Hooft coupling
proportional to $\exp(-1/g_N)$ with the dimensionless Newton coupling $g_N$.
Hence, in the asymptotically safe gravity scenario with a non-vanishing fixed
point coupling $g_N^*$, the induced 't Hooft coupling is finite at the Planck
scale, and its size depends on the chosen UV-completion. Within this scenario
the gravitational effects on anomalous $U(1)_A$-breaking at the Planck scale
may survive at low energy scales. In turn, fermion masses of the order of the
Planck scale cannot be present. This constrains the allowed asymptotically safe
UV-completion of the Gravity-QCD system. We map-out the parameter regime that
is compatible with the existence of light fermions in the low-energy regime.
