  Direct imaging observations of planets revealed that wide-orbit ($>10$ au)
giant planets exist even around subsolar-metallicity host stars and do not
require metal-rich environments for their formation. A possible formation
mechanism of wide-orbit giant planets in subsolar-metallicity environments is
the gravitational fragmentation of massive protoplanetary discs. Here, we
follow the long-term evolution of the disc for 1 Myr after its formation, which
is comparable to disc lifetime, by way of a two-dimensional thin-disc
hydrodynamic simulation with the metallicity of 0.1 ${\rm Z}_{\odot}$. We find
a giant protoplanet that survives until the end of the simulation. The
protoplanet is formed by the merger of two gaseous clumps at $\sim$0.5 Myr
after disc formation, and then it orbits $\sim$200 au from the host star for
$\sim$0.5 Myr. The protoplanet's mass is $\sim$10 ${\rm M}_{\rm J}$ at birth
and gradually decreases to 1 ${\rm M}_{\rm J}$ due to the tidal effect from the
host star. The result provides the minimum mass of 1 ${\rm M}_{\rm J}$ for
protoplanets formed by gravitational instability in a subsolar-metallicity
disc. We anticipate that the mass of a protoplanet experiencing reduced mass
loss thanks to the protoplanetary contraction in higher resolution simulations
can increase to $\sim$10 ${\rm M}_{\rm J}$. We argue that the disc
gravitational fragmentation would be a promising pathway to form wide-orbit
giant planets with masses of $\ge1$ ${\rm M}_{\rm J}$ in subsolar-metallicity
environments.
