  Let $\mu(G)$ denote the spectral radius of a graph $G$. We partly confirm a
conjecture due to Nikiforov, which is a spectral radius analogue of the
well-known Erd\H{o}s-S\'os Conjecture that any tree of order $t$ is contained
in a graph of average degree greater than $t-2$. Let
$S_{n,k}=K_{k}\vee\overline{K_{n-k}}$, and let $S_{n,k}^{+}$ be the graph
obtained from $S_{n,k}$ by adding a single edge joining two vertices of the
independent set of $S_{n,k}$. In 2010, Nikiforov conjectured that for a given
integer $k$, every graph $G$ of sufficiently large order $n$ with $\mu(G)\geq
\mu(S_{n,k}^{+})$ contains all trees of order $2k+3$, unless $G=S_{n,k}^{+}$.
We confirm this conjecture for trees with diameter at most four, with one
exception. In fact, we prove the following stronger result for $k\geq 8$. If a
graph $G$ with sufficiently large order $n$ satisfies $\mu(G)\geq \mu(S_{n,k})$
and $G\neq S_{n,k}$, then $G$ contains all trees of order $2k+3$ with diameter
at most four, except for the tree obtained from a star $K_{1,k+1}$ by
subdividing each of its $k+1$ edges once.
