"Unfortunately, he will soon be fired," Lorenzetti told rugby weekly Midi Olympique.
The 35-year-old Williams was charged last month.
Former Wallabies winger James O'Connor, who plays for Toulon, was also arrested and charged with possession.
Both players have been stood down by their clubs.
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Toulon said they had yet to make any decision about O'Connor.
"President (Mourad) Boudjellal wants to take time to think about it and will make a decision at a date he does not know yet," Toulon said in a statement to Reuters.
(Reporting by Julien Pretot; Editing by Alison Williams)
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