Early career Diallo is a graduate of the
Monaco youth academy, joining them at the age of 15. Diallo joined
Brest on loan in 2018. He made his professional debut with the club in a 1–1 (4–3) penalty shootout win in the
Coupe de la Ligue over
Sochaux on 14 August 2018.
Southampton On 4 October 2020, Diallo signed for
Premier League club
Southampton on a four-year contract, for an undisclosed fee. On 17 October 2020, Diallo made his first appearance for the club in a 3–3 draw against
Chelsea, where he came off the bench to replace
Oriol Romeu. His first Premier League start came in a 0–0 draw against
Fulham on 26 December. On 21 September 2021, Diallo scored his first professional goal, in the
EFL Cup against
Sheffield United which ended 2–2 at full time before Southampton advanced 4–2 on penalties.
Al-Duhail On 19 July 2023, Diallo signed for
Qatar Stars League club
Al-Duhail. ==Personal life==