  We revisit the charge symmetry breaking $(CSB)$ in nucleon-nucleon $(NN)$
interaction caused by $\pi$-$\eta$ mixing in nuclear matter $(NM)$ employing
one boson exchange $(OBE)$ model. The medium effect on $CSB$ is incorporated
through the in-medium $\pi$ and $\eta$ propagators. In addition, the medium
modification to the nucleon mass is also taken into account to construct the
$CSB$ class $III$ potential considering off-shell $\pi$-$\eta$ mixing amplitude
and large contribution of in-medium meson propagators to $CSB$ potential is
found for the pseudoscalar $(PS)$ interaction compared to that of pseudovector
$(PV)$ interaction.
