Radu was nominated for Gazeta Sporturilor's 2018 Romanian Footballer of the Year award in late November. On 22 December, he saved one of the two penalty kicks awarded to Atalanta in a 3–1 home victory at the Stadio Luigi Ferraris. In January 2019, he was included by UEFA.com in a list of the fifty best young footballers to watch for that year. In spite of being coached by three different managers throughout the season, Radu maintained his place as first-choice goalkeeper and amassed 33 league appearances.
In June 2019, as stipulated Genoa agreed to buy Radu for €8 million, but he was immediately redeemed by Internazionale for a reported €12 million. The deal was officially announced in July 2019, and at the same time he returned to Genoa on another loan.
Radu represented Romania at under-21 level, featuring for the side in the 2019 UEFA European Championship qualifiers. He made his debut on 13 June 2017, in a 2–0 away win over Liechtenstein. Radu captained both of the group matches in September 2018, saving a penalty to preserve a win against Portugal and keeping a clean sheet in a victory over Bosnia and Herzegovina. The following month, Tricolorii mici went on to finish top of the group and thus qualified for the final tournament for the second time in their history.
Radu was called up for the first time to the Romania senior squad for the UEFA Euro 2020 qualifiers against Norway and Malta in June 2019. Later that month, he was a starter in all three group fixtures of the UEFA Under-21 Euro in Italy, conceding three goals and keeping a clean sheet in a draw against France which secured the first place for his nation. Romania were eventually eliminated by defending champions Germany in the semi-finals, after a 2–4 loss.