  Odd radio circles (ORCs) are a newly discovered class of extended faint radio
sources of unknown origin. We report the first detection of diffuse X-ray gas
at the location of a low-redshift ORC (z=0.046) known as Cloverleaf ORC. This
observation was performed with the XMM-Newton X-ray telescope. The physical
extent of the diffuse X-ray emission corresponds to a region of approximately
230 kpc by 160 kpc, lying perpendicular to the radio emission detected by
ASKAP. The X-ray spectrum shows characteristics of thermal multiphase gas with
temperatures of 1.10+/-0.08 keV and 0.22+/-0.01 keV and a central density of
$(4.9\pm0.6)\times10^{-4}$ cm$^{-3}$, indicating that the Cloverleaf ORC
resides in a low-mass galaxy group. Using X-ray observations, with hydrostatic
equilibrium and isothermal assumptions, we measure the galaxy group to have a
gas mass and a total mass of $(7.7\pm 0.8) \times 10^{11}$ M$_{\rm sun}$ and
$2.6\pm0.3\times10^{13}$~$M_{\rm sun}$ within the overdensity radius R$_{500}$.
The presence of a high-velocity subgroup identified in optical data, the
orientation of the brightest cluster galaxy, the disturbed morphologies of
galaxies toward the east of the Cloverleaf ORC, and the irregular morphology of
the X-ray emission suggest that this system is undergoing a galaxy group
merger. The radio power of the ORC could be explained by the shock
reacceleration of fossil cosmic rays generated by a previous episode of black
hole activity in the central active galactic nucleus.
