[10] On 14 May 2016, during the last matchday of the campaign, Radu made his senior debut for Inter by entering as a 72nd-minute substitute for Juan Pablo Carrizo in a 3–1 Serie A away defeat to Sassuolo.

[21] After Federico Marchetti was used as a starter in the first four games of the 2018–19 season, Radu made his debut on 26 September against Chievo in the Serie A, managing to keep a clean sheet in the 2–0 victory.

[7] 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[22][23] and Alessio Romagnoli's late volley in a 2–1 loss to Milan on the 31st of the same month;[24] he was however encouraged by manager Ivan Jurić, who blamed young age as the source of his errors.

In June 2019, after Genoa paid the transfer fee for Radu's permanent move, he was immediately bought back by Inter Milan for €12 million.

[citation needed] Inter Milan loaned Radu out to Parma for the remainder of the 2019–20 season, but he did not play in any games during his stint at the Stadio Ennio Tardini.

[35] On 27 July 2023, Premier League side Bournemouth announced the signing of Radu from Inter on a season long-loan, with a future option to make the move permanent.

[38] 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.

In May 2019, Radu was called up to the Romania senior squad for the approaching UEFA Euro 2020 qualifiers against Norway and Malta, but was not handed his full debut.

[39] In June, he started in all three group fixtures of the UEFA Under-21 Euro in Italy, keeping a clean sheet in a draw against France which secured the first place for his nation.