Arsenal have confirmed Kieran Tierney will be out for three months after it was determined he requires surgery on a dislocated shoulder.
The Scotland international was injured on Monday against West Ham United in the 3-1 Premier League win at the London Stadium and will undergo an operation in the next week.
Tierney fell awkwardly in the 26th minute and was substituted shortly after with his arm in a makeshift sling.
The injury is yet another setback for the former Celtic player, who was one of Arsenal's major summer signings at a cost of just over £24 million.