The 18-year-old midfielder has represented France’s Under-16s and Under-17s in youth, but he is now preparing to be called up for the Tunisia national team.
Mejbri is eligible to play for Tunisia as both his parents were born in the country.
According to Goal, the young United decided to make the switch because he “feels Tunisian rather than French”.
Mejbri, who was born in Ivry-sur-Seine, France, has already turned down the opportunity to represent Under-18 and Under-19 France in recent seasons.
The Red Devils midfielder has made 12 appearances for France U16 and three appearances for U17, in qualifying matches for the European Under-17 Championship.
Mejbri arrived at Old Trafford in 2019 after United caught the much-loved youngster from Monaco.
The former Monaco youth academy product secured his first senior appearance at United on the last day of the season.
Mejbri came off the bench to replace Juan Mata in the 82nd minute of United’s 2-1 win over Wolves at Molineux.
The future Tunisia international has impressed in youth for United and has scored five times and recorded 10 assists in 26 appearances across all competitions.
Mejbri’s fantastic form helped him win United’s Under-23 Player of the Year award for the 2020-21 campaign.
“I’m going to say thank you to the coaches, my teammates and everyone who helped me. Thank you so much.
“I think the Under 23 league was good, we did well with a young team and I think we all learned some things.
“The coach helped us a lot, with our technique [play] and how we should work. For me, personally, it was good. I learned a lot. I had to be stronger.
“I was more consistent in games and had more goals and assists than the previous season. It’s always good to take this step, so it was good.