Radja Nainggolan will be out for "a while" after the midfielder was injured in Inter's derby victory against AC Milan, said Luciano Spalletti.
Nainggolan limped off after half an hour of Sunday's Serie A clash at the San Siro, where Inter won 1-0 thanks to a late Mauro Icardi header.
The former Roma star appeared to sustain the injury in a heavy tackle from Lucas Biglia that saw the Milan midfielder booked, although Nainggolan also caught the Argentina international in the incident.
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Nainggolan initially played on but after he was on the end of another firm challenge he was replaced by Borja Valero.