After Federico Marchetti was used as a starter in the first four games of the Serie A season, Radu made his debut on 26 September against Chievo, managing to keep a clean sheet in the 2–0 victory. He was deemed at fault for several goals his team conceded in the next fixtures, including Cristiano Ronaldo's opener in a 1–1 draw with Juventus on 20 October and Alessio Romagnoli's late volley in a 1–2 loss to A.C. Milan on the 31st the same month; he was however backed up by manager Ivan Jurić, who blamed young age as the cause of his errors. On 3 November, he conceded five goals from his parent club Internazionale.