The tennis star was signing autographs at the Italian Open when the object suddenly dropped from above.
Camila Giorgi abruptly retired earlier in the week, and a report from an Italian newspaper indicates Italy's financial police is looking for her.
Rafael Nadal is knocked out of the Italian Open by Hubert Hurkacz in what could be the Spaniard's final appearance in Rome.
Djokovic jokingly wore the head protection as he turned up to train at the Italian Open 24 hours after being struck by the bottle