 He made his debut for Milan on 27 August 2016, coming off the bench in the 80th minute during a 4–2 loss away against his former club Napoli.Following Riccardo Montolivo's long-term injury sustained in October 2016, Sosa assumed the role of a deep-lying playmaker, alternatively known as "regista", operating in front of the team's defense line in 4–3–3 formation.Adapting to the change of position from his usual attacking midfielder role, he cited Juan Sebastián Verón as inspiration.