  In this article, we study the notion of central extension of Leibniz
$n$-algebras relative to $n$-Lie algebras to study properties of Schur
$\mathsf{Lie}$-multiplier and $\mathsf{Lie}$-covers on Leibniz $n$-algebras. We
provide a characterization of $\mathsf{Lie}$-perfect Leibniz $n$-algebras by
means of universal $\mathsf{Lie}$-central extensions. It is also provided some
inequalities on the dimension of the Schur $\mathsf{Lie}$-multiplier of Leibniz
$n$-algebras. Analogue to Wiegold [38] and Green [17] results on groups or
Moneyhun [26] result on Lie algebras, we provide upper bounds for the dimension
of the $\mathsf{Lie}$-commutator of a Leibniz $n$-algebra with finite
dimensional $\mathsf{Lie}$-central factor, and also for the dimension of the
Schur $\mathsf{Lie}$-multiplier of a finite dimensional Leibniz $n$-algebra.
