Norbert Pap said the tomb is believed to have been built over the spot where Suleiman's tent stood and where he died.
Pap, head of the department of Political Geography, Regional and Development Studies at the University of Pecs in Hungary, said objects suggesting it was Suleiman's tomb were found during the dig, as well as other historical evidence, although more excavations are needed to confirm the find.
Until his death at age 71, Suleiman was the Ottoman Empire's longest-ruling sultan. The Turks greatly expanded their dominance in the Balkans, the Middle East and northern Africa during his 46-year reign.
What is believed to be the sultan's tomb is located in the former Ottoman settlement of Turbek, which was destroyed in the 1680s. The settlement's discovery was announced by Pap in 2013.
Szigetvar was defended by locals led by Croatian-Hungarian nobleman Miklos Zrinyi. The siege was a pyrrhic victory for the Turks and delayed their ultimately unsuccessful advance toward Vienna for decades.
Pap said some other structures near the tomb, all still underground, are likely to be a small mosque and a dervish monastery. He said excavation work at the site would restart in April.