“The club has taken the decision to relieve coach Enrique Martin Monreal of his duties,” Osasuna said in a statement.
“After analysing the sporting situation of the team, it was determined there was a need to take this decision with the objective of turning around the current run.”
Monreal played for Osasuna for over a decade in the 1970s and 80s before leading the club to promotion via the playoffs from the Segunda Division last season.
However, Saturday’s 1-0 defeat at home to Alaves left the Navarran side second bottom of the league and three points adrift of safety.