Later, in the course of the War of the League of Cognac, he fought for the French, taking part in the capture of Nonantola and in the defence of Milan.
Later he sided with the Papal States, fighting in Parma and Fiorenzuola d'Arda against the Imperial Landsknechts.
However, during the Sack of Rome when Pope Clement VII was taken prisoner by the Imperials, he took advantage to enter Rimini.
When a Papal army of 6,000 troops under cardinal Giovanni Maria Del Monte was sent against him, Sigismondo agreed to hand over the city in exchange for 6,000 ducati.
In the following year he fought as condottiero for Venice and for the Holy Roman Empire in Hungary, and travelled to Constantinople to ask support against the Papal occupation of Rimini.