  Understanding how giant planets form requires observational input from
directly imaged protoplanets. We used VLT/NACO and VLT/SPHERE to search for
companions in the transition disc of 2MASS J19005804-3645048 (hereafter CrA-9),
an accreting M0.75 dwarf with an estimated age of 1-2 Myr. We found a faint
point source at $\sim$0.7'' separation from CrA-9 ($\sim$108 au projected
separation). Our 3-epoch astrometry rejects a fixed background star with a
$5\sigma$ significance. The near-IR absolute magnitudes of the object point
towards a planetary-mass companion. However, our analysis of the 1.0-3.8$\mu$m
spectrum extracted for the companion suggests it is a young M5.5 dwarf, based
on both the 1.13-$\mu$m Na index and comparison with templates of the Montreal
Spectral Library. The observed spectrum is best reproduced with high effective
temperature ($3057^{+119}_{-36}$K) BT-DUSTY and BT-SETTL models, but the
corresponding photometric radius required to match the measured flux is only
$0.60^{+0.01}_{-0.04}$ Jovian radius. We discuss possible explanations to
reconcile our measurements, including an M-dwarf companion obscured by an
edge-on circum-secondary disc or the shock-heated part of the photosphere of an
accreting protoplanet. Follow-up observations covering a larger wavelength
range and/or at finer spectral resolution are required to discriminate these
two scenarios.
