Sunday's clash at Atalanta's Gewiss Stadium was due to kick off at 6pm local time, but it was announced a couple of hours before kickoff that the game would not go ahead.
None of Serie A, Atalanta or Fiorentina disclosed the reason for the cancellation, but various outlets have reported that the match was postponed due to concerns about the health of Viola chief Joe Barone.
According to journalist Fabrizio Romano, the 57-year-old - who turns 58 in three days' time - was immediately rushed to hospital, and it is believed that he fell ill in front of some of the Fiorentina players at the team hotel.
The players in question were subsequently too shaken to complete their on-field duties, and the game was therefore postponed until an as yet undetermined later date.
Atalanta sit sixth in the Serie A table with 47 points from their 28 fixtures, two spots and four points better off than eighth-placed Fiorentina.