Florian Lejeune has suffered a cruciate ligament injury that means the Newcastle United defender will need surgery, leaving the club in search of replacements.
Lejeune was absent for Saturday's pre-season friendly away to Porto and is set for an extended spell on the sidelines.
The 27-year-old's injury is a major blow to Newcastle given their relative lack of squad depth, although they did complete the signing of defender Fabian Schar from Deportivo La Coruna this week.
They have also signed Japan international striker Yoshinori Muto from Mainz, subject to a work permit.