The former premier was convicted last Friday of tax evasion and issued the threat Saturday, Italy's ANSA news agency reported Thursday.
Berlusconi said even though his center-right People of Freedom party would not actively work against Monti, "we are convinced that austerity measures imposed by the European Union have put the economy on an endless, downward spiral."
Italy's financial crisis forced Berlusconi to resign last year.
Berlusconi's threat had drawn criticism from within his own party.
House whip Fabrizio Cicchitto said attempts to bring down the government could shake investor confidence and cause Italy's borrowing rates to go up.
Party secretary Angelino Alfano distanced himself from Berlusconi's remarks Monday, stirring rumors of a party fracture if the ex-premier carried out his threat.
An Italian newspaper said Alfano's stance had angered Berlusconi but early Thursday he issued a statement denying any rift.
In the statement, Berlusconi confirmed "his close relationship of trust and affection" with Alfano.