Onana joined Inter Milan on a free transfer in July 2022, winning a Coppa Italia and Supercoppa Italiana title in his sole season at the club, also reaching the Champions League final.

He kept a clean sheet as United won the game 1–0,[30] but was at the centre of controversy after referee Simon Hooper and VAR Michael Salisbury opted not to award a late penalty for a foul by Onana on Saša Kalajdžić.

[31] On 20 September, following a 4–3 defeat against Bayern Munich in the Champions League opening fixture, Onana said he had "let the team down" following mistakes during the match.

[33] Ten Hag later said that Onana should be inspired by Manchester United's legendary goalkeepers Peter Schmeichel and David de Gea.

[34] On 24 October 2023, he saved a penalty in the 97th minute in a Champions League match which ended in a 1–0 victory against Copenhagen, leading to his club's first win in the competition that season.

The BBC called it "a night of suffering for Onana", who "produced a horror show to undermine much of United's good work", while the Manchester Evening News declared he "carelessly conceded" the first Galatasaray goal, "catastrophically fumbled" the second and "too easily beaten" for the third.

[37][38][39] He was defended by manager Erik ten Hag, who opined that Onana's stats showed him to be the second-best goalkeeper in the Premier League.

[42] During his second season, by December 2024 Onana had kept more clean sheets than any other Premier League goalkeeper, but was criticised for making some mistakes against Nottingham Forest and FC Viktoria Plzeň.

[47] He played the first match against Switzerland, before being dropped in the second against Serbia, then he was eventually sent home from the tournament on 28 November by manager Rigobert Song due to a disciplinary issue related to arguments about the latter's coaching tactics.

[50] Just over eight months later, on 29 August 2023, Onana was recalled into the Cameroon squad by Rigobert Song for an Africa Cup of Nations qualification match against Burundi.

[51] The goalkeeper formally confirmed his return to international football several days later, on 4 September, via a message posted on social media, stating that, "in the face of manipulation, lies and abuse of power", he had chosen to "stay loyal to my principle, representing with pride a country that deserves our sincere commitment.