  Muon-spin rotation data collected at ambient pressure ($p$) and at $p=2.42$
GPa in MnP were analyzed to check their consistency with various low- and
high-pressure magnetic structures reported in the literature. Our analysis
confirms that in MnP the low-temperature and low-pressure helimagnetic phase is
characterised by an increased value of the average magnetic moment compared to
the high-temperature ferromagnetic phase. An elliptical double-helical
structure with a propagation vector ${\bf Q}=(0,0,0.117)$, an $a-$axis moment
elongated by approximately 18% and an additional tilt of the rotation plane
towards $c-$direction by $\simeq 4-8^{\rm o}$ leads to a good agreement between
the theory and the experiment. The analysis of the high-pressure $\mu$SR data
reveals that the new magnetic order appearing for pressures exceeding $1.5$ GPa
can not be described by keeping the propagation vector ${\bf Q} \parallel c$.
Even the extreme case -- decoupling the double-helical structure into four
individual helices -- remains inconsistent with the experiment. It is shown
that the high-pressure magnetic phase which is a precursor of superconductivity
is an incommensurate helical state with ${\bf Q} \parallel b$.
