Arsenal midfielder Jack Wilshere will require surgery on a hairline fracture in his left leg and is set for several weeks of rehabilitation.
Manager Arsene Wenger last week confirmed the England international had suffered a "little setback" in his scheduled recovery from the injury sustained in pre-season.
It is understood following further medical examinations, the decision has now been taken that an operation is needed to properly correct the problem and is likely to take place in the next few days.
The news will come as a blow to both the player, who has battled through a string of fitness issues in recent seasons, and club, with forward Danny Welbeck also set for an extended spell on the sidelines until at least Christmas following knee surgery.
Arsenal travel to Croatia for their Champions League opener against Dinamo Zagreb on the back of a 2-0 home win over Stoke which sustained their recovery in the Barclays Premier League.
Forward Theo Walcott, who once netted a hat-trick playing for England at the Maksimir Stadium, is pressing for another start after scoring the opening goal against the Potters on Saturday.
Defender Per Mertesacker is not expected to be involved having just recovered from a virus and also being involved in a minor road traffic accident on Monday.