The combined work of M.
Aschbacher, G. Seitz, and I. Miyamoto classified finite groups G with a standard
subgroup L isomorphic to PSU(4,2n) such that either n > 1 or CG(L) has noncyclic
Sylow 2-subgroups. In this paper, we study the case that n = 1 and CG(L) has cyclic
Sylow 2-subgroups.