"Too many issues are under investigation," Moshe Ya'alon told CNN's Christiane Amanpour in an interview set to air Tuesday night. "I believe that at the end we will witness indictment."
Israeli police are conducting two investigations linked directly to Netanyahu. A third involves defense procurement conducted during his premiership.
Netanyahu has been questioned several times in connection with the first two investigations -- over suggestions he inappropriately accepted gifts from businessmen overseas and over accusations he made a deal with Arnon Mozes, owner of one of Israel's leading newspapers, Yedioth Ahronoth. That agreement allegedly involved the newspaper toning down its attacks on the Prime Minister in exchange for Netanyahu ensuring that circulation of a rival paper was reduced.
Netanyahu's lawyer has told CNN he does not believe Israel's Attorney General will choose to indict the Prime Minister in connection with either of those cases. Netanyahu has repeatedly denied wrongdoing.
The third case under investigation involves the purchase of German submarines and attack boats. The procurements were made during Netanyahu's premiership, but so far he has not been questioned and the Attorney General has said he is not a target of the investigation.
The decision to buy the German naval vessels in 2015 was opposed by Ya'alon, who was serving at the time as Netanyahu's Defense Minister.
Ya'alon later was replaced at the Defense Ministry and chose to resign from the government altogether, citing "difficult moral and professional controversies with the Prime Minister, a number of other ministers, and some members of Knesset."
He has since announced his intention to form his own political party to challenge Netanyahu.
In response to Ya'alon's comments to CNN, an official in the Prime Minister's Office said: "Mr. Ya'alon's allegations are baseless. Unfortunately, he has turned political differences into a smear campaign against the Prime Minister. For example, he has tried to taint Prime Minister Netanyahu's decisions on defense purchasing, but the attorney general's office has explicitly stated that the Prime Minister wasn't even under investigation in this matter. The Prime Minister is guided by one overriding consideration: ensuring the security of Israel."
Ya'alon told CNN that he and Netanyahu do share similar views on security and foreign affairs, but he remains critical of the Prime Minister in other areas.
"My main dispute with my Prime Minister, as well as other members of the government and the coalition, was about internal issues," he said.
"I am not proud of the fact that we have corruption. I am very proud of the fact that the rule of law is dominating, and the law enforcement authorities are independent to investigate everyone, to include the Prime Minister."