The Premier League duo were set to feature Italy's upcoming European Championship qualifiers against Malta and England but the Italian Federation have now confirmed their release from the training camp.
Italian news agency ANSA have reported that both Tonali and Zaniolo have been questioned relating to an illegal betting probe.
A statement from the Italian Federation read: "The Federation announces that this afternoon the Turin Public Prosecutor's Office has conducted investigations into players, Sandro Tonali and Nicolo Zaniolo, who are currently training with the national team at the Coverciano Federal Training Centre.
"Regardless of the nature of the events, considering that the two players are not in the necessary condition to face the matches scheduled for the next few days, the Federation has decided, also for their protection, to allow them to return to their respective clubs."
FIGC prosecutors earlier this week announced an investigation into 22-year-old Juventus midfielder Nicolo Fagioli.