  For the long standing low mass puzzle of $\Lambda_c(2940)^+$, we propose an
unquenched picture. Our calculation explicitly shows that the mass of the
$\Lambda_c(2P,3/2^-)$ state can be lowered down to be consistent with the
experimental data of $\Lambda_c(2940)^+$ by introducing the $D^*N$ channel
contribution. Additionally, we give a semi-quantitative analysis to illustrate
why the $\Lambda_c(2940)^+$ state has a narrow width. It means that the low
mass puzzle of $\Lambda_c(2940)^+$ can be solved. What is more important is
that we predict a mass inversion relation for the $2P$ $\Lambda_{c}^+$ states,
i.e., the $\Lambda_c(2P,1/2^-)$ state is higher than the $\Lambda_c(2P,3/2^-)$,
which is totally different from the result of conventional quenched quark
model. It provides a criterion to test such an unquenched scenario for
$\Lambda_c(2940)^+$. We expect the future experimental progress from the LHCb
and Belle II.
