  We analyzed multiwavelength observations of the previously identified
Galactic center X-ray binary CXO 174528.79-290942.8 (XID 6592) and determine
that the near-infrared counterpart is a red supergiant based on its spectrum
and luminosity. Scutum X-1 is the only previously known X-ray binary with a red
supergiant donor star and closely resembles XID 6592 in terms of X-ray
luminosity (L$_{\mathrm{X}}$), absolute magnitude, and IR variability
(L$_{\mathrm{IR,var}}$), supporting the conclusion that XID 6592 contains a red
supergiant donor star. The XID 6592 infrared counterpart shows variability of
$\sim$0.5 mag in the Wide-field Infrared Survey Explorer-1 band (3.4 $\mu$m) on
timescales of a few hours. Other infrared data sets also show large-amplitude
variability from this source at earlier epochs but do not show significant
variability in recent data. We do not expect red supergiants to vary by
$\sim50\%$ in luminosity over these short timescales, indicating that the
variability should be powered by the compact object. However, the X-ray
luminosity of this system is typically $\sim1000\times$ less than the variable
luminosity in the infrared and falls below the Chandra detection limit. While
X-ray reprocessing can produce large-amplitude fast infrared variability, it
typically requires L$_{{\mathrm{X}}} >> $ L$_{\mathrm{IR,var}}$ to do so,
indicating that another process must be at work. We suggest that this system
may be a supergiant fast X-ray transient (SFXT), and that a large
($\sim10^{38}$ ergs s$^{-1}$), fast ($10^{2-4}$ s) X-ray flare could explain
the rapid IR variability and lack of a long-lasting X-ray outburst detection.
SFXTs are normally associated with blue supergiant companions, so if confirmed,
XID 6592 would be the first red supergiant SFXT, as well as the second X-ray
red supergiant binary.
