We study the spontaneous decay rate of a single molecule close to a metallic nanoparticle in the extreme near‐field regime. The electrodynamic response of the metal is modelled using a non‐local dielectric constant, that accounts for the relevant microscopic length scales. We describe quantitatively the crossover between the macroscopic and microscopic regimes. In the case of silver, for a nanoparticle with radius 25 nm, the transition occurs for a distance between the emitter and the metal surface on the order of 10 nm. We show that below this distance, the non‐radiative decay rate and the quenching efficiency are enhanced due to the non‐local interaction.