The presence of a small-mass planet (Mp < 0.1 MJup) seems, to date, not to depend on metallicity, however, theoretical simulations have shown that stars with subsolar metallicities may be favoured for harbouring smaller planets. In this paper, we present the analysis of HD?175607, an old G6 star with metallicity Fe/H = -0.62. We gathered 119 radial velocity measurements in 110 nights over a time span of more than nine years. The radial velocities were analysed using Lomb-Scargle periodograms, a genetic algorithm, a Markov chain Monte Carlo analysis, and a Gaussian processes analysis. The spectra were also used to derive stellar properties. Several activity indicators were analysed to study the effect of stellar activity on the radial velocities. We find evidence for the presence of a small Neptune-mass planet orbiting this star with an orbital period P = 29.01 + or - 0.02 days in a slightly eccentric orbit. HD175607 is the most metal-poor FGK dwarf with a detected low-mass planet amongst the currently known planet hosts.