His model at the time was Boccioni, but he was also attentive to the painting of Gaetano Previati, Carlo Carrŕ, who was a friend of his father, and the Constructivist Giandante X. He became familiar with the works of Picasso and Cézanne through reproductions; other important occasions for his formation as an artist, besides visits to the Pinacoteca di Brera, were the manifestations of the Futurist avant-garde, from the "noisemaking" shows of Luigi Russolo to Enrico Prampolini’s pantomimes.

With Bruno Munari in 1928 he signed the Manifesto of "Dynamism and Muscular Reform" painting, in which he theorized a search, in art, for new, antinaturalistic dynamic forms.

With this artistic choice Sassu was aiming at a solid possession of the forms, in contrast with the loss on the part of the younger Futurists of that direct grasp of nature and things which he felt to be instead the distinguishing trait of the "classical" Boccioni. His graphic work in this same period reveals the artist’s specific interest in markedly "modern" themes: sports, machines, industry.

Futurism was by now passé, and Sassu, like his new companions, was moving towards a "taste for the primitives," an archaic style, with his new drawings and landscape and figure paintings centering on the theme of the city and its modern industrial outskirts. The line of modernism emerged also in his first painting with a sacred subject, a Last Supper brought up to date and set in today’s world, in an outlying industrial area.