  Let $F$ be a locally compact non-archimedean field of residue characteristic
$p$, $\textbf{G}$ a connected reductive group over $F$, and $R$ a field of
characteristic $p$. When $R$ is algebraically closed, the irreducible
admissible $R$-representations of $G=\textbf{G}(F)$ are classified in term of
supersingular $R$-representations of the Levi subgroups of $G$ and parabolic
induction; there is a similar classification for the simple modules of the
pro-$p$ Iwahori Hecke $R$-algebra. In this paper, we show that both
classifications hold true when $R$ is not algebraically closed.
