La Viola are reportedly ready to give the 21-year-old an ultimatum after their Sporting Director Daniele Prade declared his frustrations over the delay in signing.
Ljajic has been linked with a move to Manchester City and AC Milan in the summer, but is believed to be happy to stay in Florence, and Prade wants the issue resolved.
"We are trying to extend the Ljajic's contract but it depends on the player and his will," Prade said.
"There will be an important meeting between his agent and our president, but our club wants only motivated people who are willing to stay at Fiorentina.
"We have to evaluate this situation day by day."