  An ultraluminous X-ray source (ULX) in NGC 5252 has been known as a strong
candidate for an off-nuclear intermediate-mass black hole. We present
near-infrared imaging data of the ULX obtained with the William Herschel
Telescope. Using this data we estimate a stellar mass associated with the ULX
of $\approx 10^{7.9\pm0.1}M_{\rm \odot}$ , suggesting that it could be (the
remnant of) a dwarf galaxy that is in the process of merging with NGC 5252.
Based on a correlation between the mass of the central black hole (BH) and host
galaxy, the ULX is powered by a $10^5M_{\rm \odot}$ black hole. Alternatively,
if the BH mass is $\approx 10^6M_{\rm \odot}$ or larger, the host galaxy of the
ULX must have been heavily stripped during the merger. The ULX $K_s$-band
luminosity is two orders of magnitude smaller than that expected from an
ordinary active galactic nucleus with the observed [O III] luminosity, which
also suggests the ULX lacks a dusty torus. We discuss how these findings
provide suggestive evidence that the ULX is hosting an intermediate-mass black
hole.
