Amad Diallo was seen on crutches after Manchester United's preseason win against Arsenal.
Amad was a halftime substitute, but lasted only ten minutes.
The winger broke down with an ankle injury and was taken off via a medical buggy.
He was later seen on crutches with early reports suggesting Amad has suffered a twisted ankle. Strapping was delivered to his ankle.
United's youngsters face Wrexham in San Diego on Tuesday before the senior team play Real Madrid in Houston on Wednesday.