Let
$D$ be the
$n$-dimensional Lie ball and let
$B\text{(S)}$ be the space of hyperfunctions on the Shilov boundary
$S$ of
$D$. The aim of this paper is to give a necessary and sufficient condition on the generalized Poisson transform
${{P}_{l,\text{ }\!\!\lambda\!\!\text{ }}}f$ of an element
$f$ in the space
$B\text{(S)}$ for
$f$ to be in
${{L}^{p}}\left( S \right)$,
$1\,<\,p\,<\,\infty $. Namely, if
$F$ is the Poisson transform of some
$f\in \,B(S)$
$F\,=\,{{P}_{l,\lambda }}f$), then for any
$l\,\in \,Z$) and
$\lambda \,\in \,C$ such that
$Re[\text{i}\lambda ] > \frac{n}{2}\,-\,1$, we show that
$f\,\in \,{{L}^{p}}\text{(}S\text{)}$ if and only if
$f$ satisfies the growth condition
$${{\left\| F \right\|}_{\lambda ,p}}=\underset{0\le r<1}{\mathop{\sup }}\,{{\left( 1\,-\,{{r}^{2}} \right)}^{\operatorname{Re}\left[ \text{i }\lambda \text{ } \right]-\frac{n}{2}+l}}{{\left[ \,\int_{s}{{{\left| F\left( ru \right) \right|}^{p}}du} \right]}^{\frac{1}{p}}}<\,+\infty $$