The club of former Bayern Munich star David Alaba announced Runjaic's departure on Monday evening and thanked the 55-year-old for a spell "marked by significant successes".
With just five points from their first ten matches of the current Serie A season, Runjaic's side have struggled. Udinese, who have played in the top flight continuously for more than 30 years, sit 19th after last Saturday's 5-2 home defeat to AS Roma.
Runjaic moved from Legia Warsaw to Udine in 2024 and led the club into the top half of the table for the first time in more than ten years. Paolo Zanetti, who has previously coached Verona, Empoli and Venezia in Serie A, is being touted as his successor.
Before his move to Udine, the Austrian-born coach had worked as a head coach in Germany, including at Darmstadt 98, MSV Duisburg, 1. FC Kaiserslautern and 1860 Munich.