*Club domestic league appearances and goals, correct as of 10:24, 28 November 2024 (UTC) ‡ National team caps and goals, correct as of 13:28, 17 November 2024 (UTC)
Mengi joined the Manchester United youth system at the age of seven.[4] He made his first appearance for the club in an under-18 Premier League match against Sunderland on 28 October 2017.[5] He signed his first professional contract in September 2019.[6] He played three games for the under-21s in the 2019–20 EFL Trophy, making his debut against Lincoln City on 1 October.[7] Soon after, he was an unused substitute for the United senior team for the first time in a Europa League match against Astana on 28 November.[8]
Mengi made his senior debut on 5 August 2020, coming on as an 84th-minute substitute for Timothy Fosu-Mensah in a UEFA Europa League match against LASK.[9] Mengi was promoted to the first team on 17 September ahead of the 2020–21 season,[10] but although he was included as a substitute for EFL Cup games and on an expanded bench in the UEFA Champions League, he did not appear again for the first team in 2020.
Loans to Derby County and Birmingham City
In February 2021, he was sent on loan to EFL Championship club Derby County, managed by former United captain Wayne Rooney, for the remainder of the 2020–21 season.[11] In March, he signed a new contract with Manchester United until June 2024, with the option of another year.[4] After suffering an injury in April, Mengi returned to United early from Derby.[12] Mengi joined another Championship club, Birmingham City, in January 2022 on loan for the rest of the 2021–22 season.[13] He impressed,[14] but a recurring hamstring injury restricted him to just ten appearances.[15][16]
Luton Town
On 31 August 2023, Mengi joined newly promoted Premier League club Luton Town for an undisclosed fee, signing a long-term contract.[17] He scored the first goal of his senior career on 25 November to give Luton the lead against Crystal Palace; although Palace equalised immediately afterwards, Jacob Brown secured Luton's first home win of the Premier League season.[18]