Pioli led – not least together with Zlatan Ibrahimovic – Milan to league victory a few years ago.
Lately, the jobs haven't been long-term. After just one season at Saudi Al-Nassr, he took the job at Fiorentina, sixth last season in Serie A.
Daniele Galloppa will take over until further notice.
Piolo, 60, is the third Serie A coach to be sacked this autumn, following Igor Tudor's departure from Juventus and Patrick Vieira's dismissal at Genoa.
