The measurement of Z-boson production in Pb--Pb collisions at \fivenn is reported. It is performed in the dimuon decay channel, through the detection of muons with pseudorapidity $-4 < \eta_{\mu} < -2.5$ and transverse momentum $\pt^{\mu} > 20$ \GeVc. The invariant yield is measured for opposite-sign dimuons with invariant mass $60 < \mmumu < 120$ \GeVmass and rapidity $2.5 < y^{\mu\mu} < 4$. The yield is also presented as a function of rapidity and centrality. The results are compared with theoretical calculations, both with and without nuclear modifications to the Parton Distribution Functions (PDFs). A $3.4\sigma$ deviation is seen in the integrated yield between the data and calculations based on the free-nucleon PDFs, while good agreement is found once nuclear modifications are considered.