  We present deep observations of the field of the magnetar CXOJ164710.2-455216
in the star cluster Westerlund 1, obtained in the near-infrared with the
adaptive optics camera NACO@VLT. We detected a possible candidate counterpart
at the {\em Chandra} position of the magnetar, of magnitudes $\mathrm{J} = 23.5
\pm 0.2$, $\mathrm{H} = 21.0 \pm 0.1$, and $\mathrm{K}_\mathrm{S} = 20.4 \pm
0.1$. The K$_{\rm S}$-band measurements available for two epochs (2006 and
2013) do not show significant signs of variability but only a marginal
indication that the flux varied (at the 2 $\sigma$ level), consistent with the
fact that the observations were taken when CXOJ164710.2-455216 was in
quiescence. At the same time, we also present colour--magnitude and
colour--colour diagrams in the J, H, and K$_{\rm S}$ bands from the 2006 epoch
only, the only one with observations in all three bands, showing that the
candidate counterpart lies in the main bulk of objects describing a relatively
well--defined sequence. Therefore, based on its colours and lack of
variability, we cannot yet associate the candidate counterpart to
CXOJ164710.2-455216. Future near-infrared observations of the field,
following-up a source outburst, would be crucial to confirm the association
from the detection of near-infrared variability and colour evolution.
