  We assess the impact of Galactic synchrotron foreground removal on the
observation of high-redshift quasar HII regions in redshifted 21-cm emission.
We consider the case where a quasar is observed in an intergalactic medium
(IGM) whose ionisation structure evolves slowly relative to the light crossing
time of the HII region, as well as the case where the evolution is rapid. The
latter case is expected towards the end of the reionisation era where the
highest redshift luminous quasars will be observed. In the absence of
foregrounds the fraction of neutral hydrogen in the IGM could be measured
directly from the contrast between the HII region and surrounding IGM. However,
we find that foreground removal lowers the observed contrast between the HII
region and the IGM. This indicates that measurement of the neutral fraction
would require modelling to correct for this systematic effect. On the other
hand, foreground removal does not modify the most prominent features of the
21-cm maps. Using a simple algorithm we demonstrate that measurements of the
size and shape of observed HII regions will not be affected by continuum
foreground removal. Moreover, measurements of these quantities will not be
adversely affected by the presence of a rapidly evolving IGM.
