 As a lieutenant to his cousin, the condottiero Gian Giacomo Medici (known as Medeghino), in the fall of 1531, Serbelloni fought against the Sforza militias and the imperial forces of Charles V, who later became his lord and employer.A few weeks later, he took part in the defence of Lecco together with Niccolò Pelliccione.Later on still he followed his cousin into exile in Piedmont, in the service of the Duke of Savoy.