Guerreiro suffered an injury to his ankle in Portugal’s second match against Russia at the Confederations Cup, with head coach Fernando Santos later stating that he had suffered a fracture.
The 23-year-old later claimed that the broken bone was an old issue and Portugal downgraded the injury to bruising, although he missed the remainder of the tournament.
However, Dortmund have confirmed that subsequent medical checks have identified “a clear break”, meaning Guerreiro will be out of action until at least October.
“German Cup winners Borussia Dortmund will be without Raphael Guerreiro for between three and four months,” the club said in a statement. “The 23-year-old underwent a foot operation today and is now set for a lengthy spell on the sidelines.
“Guerreiro sustained the injury while playing for European champions Portugal in a Confederations Cup group stage match against hosts Russia. BVB were subsequently assured by the Portuguese Football Association that the 23-year-old had only sustained a bruised foot.
“However, examinations conducted in Dortmund have now revealed that the foot of the Portugal international has suffered a clear break.
“Guerreiro, who made 35 appearances for Borussia Dortmund in the Bundesliga, the DFB Cup and the UEFA Champions League last season, scoring nine goals and setting up a further nine, will be out until October/November following the surgery.”