Radoslav Čelnik (Serbian Cyrillic: Радослав Челник) was a Serbianduke (Voivode) of Srem in the 16th century. At first, Radoslav Čelnik was a general commander of Emperor Jovan Nenad's army. In 1527, when Emperor Jovan Nenad was murdered and his army was dispersed, Radoslav Čelnik, together with part of the former emperor's army moved from Bačka to Srem and acceded into the Ottoman service. Radoslav Čelnik then ruled over Srem as an Ottoman vassal and took for himself the title of the duke of Srem, while his residence was in Slankamen.
Being an Ottoman vassal, Radoslav Čelnik also secretly kept the connection with Habsburgs. When the Ottoman army passed through Srem, Radoslav Čelnik moved to Habsburg territory, but when the Ottomans returned from their foray, Radoslav Čelnik also returned to Srem. However, after this return, he did no longer ruled over entire Srem, and his residence was no more in Slankamen, but in the town named Nebojc, on the river Vuka near Vukovar. In 1530, he made agreement with the Habsburgs, and moved from Srem to Habsburg territory, publicly concluded his alliance with Ottomans, and acceded into Habsburg service.