The agreement includes an obligation to buy worth around £21.4 million (€25m), which will become active if the Romanian international meets certain appearance-related conditions during the campaign.
Reports suggest the clause could be triggered if Dragusin makes 22 appearances of at least 45 minutes each.
Tottenham have also secured a 10 per cent sell-on clause on any future profit made from a subsequent transfer.
The 23-year-old joined Spurs from Genoa in January 2024 and went on to make 48 appearances in all competitions.
A regular for Romania, Dragusin has earned 30 international caps and will now continue his career in Serie A with Fiorentina.