I recommend Clinica del Dr Avanzi, with several branches in town. Dr Avanzi is a well known traumatologist expert in sports (deportologo), professional sport people are his patients, and also run a not for profit clinic, where you ask for an appointment saying which part of the body you need to be seen (knee, hip, etc). Most of the doctors speak fluent English, Dr Avanzi for sure, as he is in international sport traumatologists associations. There is an emergency room at their branch next to Velez Stadium (flores neighbourhood) on Mondays, where you go without an appointment.