  We extend the so-called universal potential estimates of the Kuusi-Mingione
type (J.Funct. Anal. 2012) to the singular case $1<p\leq 2-1/n$ for the
quasilinear equation with measure data
  \begin{equation*}
  -\operatorname{div}(A(x,\nabla u))=\mu
  \end{equation*} in a bounded open subset $\Omega$ of $\mathbb{R}^n$, $n\geq
2$, with a finite signed measure $\mu$ in $\Omega$. The operator
$\operatorname{div}(A(x,\nabla u))$ is modeled after the $p$-Laplacian
$\Delta_p u:= {\rm div}\, (|\nabla u|^{p-2}\nabla u)$, where the nonlinearity
$A(x, \xi)$ ($x, \xi \in \mathbb{R}^n$) is assumed to satisfy natural growth
and monotonicity conditions of order $p$, as well as certain additional
regularity conditions in the $x$-variable.
