Luciano Spalletti said three Inter players asked to be substituted at half-time as he criticised AC Milan's physical approach after star midfielder Radja Nainggolan was injured.
Inter claimed a last-gasp 1-0 Serie A victory over Milan thanks to Mauro Icardi's 92nd-minute header at San Siro but Sunday's derby success appears to have come at a cost.
Spalletti fears Nainggolan could be sidelined for "a while" after the Belgian limped off following a heavy tackle from Milan's Lucas Biglia.
Biglia went on to defend the challenge, saying VAR would have vindicated him as he received a yellow card for the incident.