Unlike his predecessors, al-Nu'man was scarcely concerned with the Lakhmids' traditional Arab rivals, the Ghassanids, as the latter had fallen out with their Byzantine overlords in and been eliminated as a power factor in the region. The only recorded military activity of al-Nu'man is an attack on the Byzantine fortress of Circesium during the Byzantine–Sasanian War of 572–591. According to Arab accounts, al-Nu'man gave refuge to Hormizd's son, Khosrow II (), during his flight from the usurper Bahram Chobin in 590, and fought alongside him in a battle at al-Nahrawan against the usurper's forces.