Ultra-diffuse galaxies (UDGs) are attractive candidates to probe cosmological models and test theories of galaxy formation at low masses; however, they are difficult to detect because of their low surface brightness. In the Local Group (LG) a handful of UDGs have been found to date, most of which are satellites of the Milky Way and M31, and only two are isolated galaxies. It is unclear whether so few UDGs are expected. We address this by studying the population of UDGs formed in hydrodynamic constrained simulations of the LG from the HESTIA suite. For a LG with mass $M_{\rm LG}\!\left(<2.5\, {\rm Mpc}\right)=8\times10^{12}{\rm M_\odot}$, we predict that there are $12\pm3$ UDGs (68 per cent confidence) with stellar masses $10^6 \leq M_\ast\, /\, {\rm M_\odot} < 10^9$, and effective radii $R_{\rm e} \geq 1.5\, {\rm kpc}$, in the field of the LG, of which $2^{+2}_{-1}$ (68 per cent confidence) are detectable in the footprint of the Sloan Digital Sky Survey (SDSS). Accounting for survey incompleteness, we find that up to 82, 90, and 100 per cent of all UDGs in the LG field would be observable in a future all-sky survey with a depth similar to the SDSS, the Dark Energy Survey, or the Legacy Survey of Space and Time, respectively. Our results suggest that there is a population of UDGs in the LG awaiting discovery.