The 36-year-old's deal with Fiorentina ended at the start of this month.
Toni has played for some of Europe's biggest teams, including Juventus and Bayern Munich where he won two German league and cup doubles.
Last season he scored eight Serie A goals for Fiorentina in his second spell at the club as they just missed out on a Champions League place.
Verona, who won the league title in 1985, are back in the top flight for the first time in 11 years after finishing second in Serie B behind Sassuolo.
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