Newcastle defender Florian Lejeune could be facing a long spell on the sidelines after suffering a ligament injury.
Lejeune played in Newcastle's first pre-season game against St Patrick's Athletic but he was absent for Tuesday's draw at Hull.
He did not fly out to Portugal with the rest of the squad for Saturday's friendly against Porto.
Speaking after the 0-0 draw, Rafael Benitez said: "He will need an operation, we need to decide exactly when.
"We could lose him for a while. Bad news for us."
Lejeune was signed from Eibar last summer and the Frenchman made 24 appearances last season.
He said on Twitter: "During my last training session, I left the field due to an injury. After further medical examination the doctor told me I have a cruciate ligament injury.
"I'll have surgery in the next few days and I'll do everything to get back as quickly as possible."