The 24-year-old Beelen collided with Gent's Helio Varela and immediately seemed in bad shape. Players of both sides retreated to the dressing rooms after being shocked at the injury. Beelen received surgery the same night, which the club called "successful" in a statement released on Monday.
Feyenoord have not disclosed the severity of the injury nor given a timetable for Beelen's return.
Watanabe close
Beelen's injury has prompted Feyenoord to put pressure behind a transfer for a central defender. Vice-captain David Hancko is on the verge of joining Saudi Pro League side Al Nassr for a club record fee of €40 million.
Gent's Tsuyoshi Watanabe has been picked as Hancko's successor and is reportedly close to joining Feyenoord. According to De Telegraaf, Gent are demanding €8 million for 28-year-old Japanese international.