In the current work we explore the applicability of standard theoretical models of accretion to the observed properties of M51 ULX-7 \xspace .
The spin-up rate and observed X-ray luminosity are evidence of a neutron star with a surface magnetic field of 2 - 7 \times 10 ^ { 13 } G , rotating near equilibrium .
Analysis of the X-ray light-curve of the system ( Swift \xspace /XRT data ) reveals the presence of a \sim 39 d super-orbital period .
We argue that the super-orbital periodicity is due to disc precession , and that material is accreted onto the neutron star at a constant rate throughout it .
Moreover , by attributing this modulation to the free precession of the neutron star we estimate a surface magnetic field strength of 3 - 4 \times 10 ^ { 13 } G. The agreement of these two independent estimates provide strong constraints on the surface polar magnetic field strength of the neutron star .