The Viola have clinched just one win in their last five games and Thursday's 1-1 draw with Bologna dropped them to 15th in the table, five points clear of the drop zone.
"We need to find something extra, some fury or some competitive ruthlessness that, above all in periods when luck does not go our way, can make the difference," Mihajlovic said.
"We must react and start climbing up in the standings, starting on Sunday."
Fiorentina have been distracted by the ongoing saga over the future of Adrian Mutu.
The Romanian winger did not feature in Fiorentina's first game of the year.
Mutu has sought a move away from the Viola in January and several Serie A clubs, including Bologna, are interested in him.
"Mutu excluded himself from the squad," Mihajlovic said. "He should have played against Bologna but in the last practise session ahead of the game he left training early after finding out that the club no longer wanted to sell him.
"I cannot accept that behaviour because he has shown a lack of respect towards me and the club."
Rivals Brescia are also looking to spark their season into life.
Thursday's 2-1 defeat to Cesena marked their 11th loss of the campaign and dropped Brescia to 18th place, three points from safety.
Brescia have clinched just one win in their last 14 league games and coach Mario Beretta will be desperate for an improved performance from his players, especially in front of goal.
The Rondinelle have found the back of the net just twice in their last seven games.
Fiorentina welcome back midfielder Marco Donadel from suspension but are without the services of Per Koldrup, who serves a one-match ban.