  The characterisation of the stellar population toward young high-mass
star-forming regions allows to constrain fundamental cluster properties like
distance and age. These are essential when using high-mass clusters as probes
to conduct Galactic studies. NGC 7538 is a star-forming region with an embedded
stellar population only unearthed in the near-infrared. We present the first
near-infrared spectro-photometric study of the candidate high-mass stellar
content in NGC 7538. We obtained H and K spectra of 21 sources with both the
multi-object and long-slit modes of LIRIS at the WHT, and complement these data
with sub-arcsecond JHKs photometry of the region using the imaging mode of the
same instrument. We find a wide variety of objects within the studied stellar
population of NGC 7538. Our results discriminate between a stellar population
associated to the HII region, but not contained within its extent, and several
pockets of more recent star formation. We report the detection of CO bandhead
emission toward several sources as well as other features indicative of a young
stellar nature. We infer a spectro-photometric distance of 2.7+-0.5 kpc, an age
spread in the range 0.5-2.2 Myr and a total mass ~1.7x10^3 Msun for the older
population.
