The teenage striker was injured during Vitesse's training camp in Portugal as the club prepare for the resumption of De Eredivisie.
Rojer was operated on immediately upon his return to Holland and the 18-year-old could be out of action for several months.
The promising forward only made his Vitesse debut in the final game before the winter break.
He started in the 1-0 defeat to PSV Eindhoven but his prospects of nailing down a regular place in the team have been dealt a crushing blow.
