  AD Leonis is a nearby magnetically active M dwarf. We find Doppler
variability with a period of 2.23 days as well as photometric signals: (1) a
short period signal which is similar to the radial velocity signal albeit with
considerable variability; and (2) a long term activity cycle of 4070$\pm$120
days. We examine the short-term photometric signal in the available ASAS and
MOST photometry and find that the signal is not consistently present and varies
considerably as a function of time. This signal undergoes a phase change of
roughly 0.8 rad when considering the first and second halves of the MOST data
set which are separated in median time by 3.38 days. In contrast, the Doppler
signal is stable in the combined HARPS and HIRES radial velocities for over
4700 days and does not appear to vary in time in amplitude, phase, period or as
a function of extracted wavelength. We consider a variety of star-spot
scenarios and find it challenging to simultaneously explain the rapidly varying
photometric signal and the stable radial velocity signal as being caused by
starspots co-rotating on the stellar surface. This suggests that the origin of
the Doppler periodicity might be the gravitational tug of a planet orbiting the
star in spin-orbit resonance. For such a scenario and no spin-orbit
misalignment, the measured $v \sin i$ indicates an inclination angle of
15.5$\pm$2.5 deg and a planetary companion mass of 0.237$\pm$0.047 M$_{\rm
Jup}$.
