In the lower-left menu, select Party Management. There will be a list of praetorians that need treatment on the left side of the screen if you click on the Triage tab. The praetorian can be treated either in the legion camp or on the field if the player has a doctor with him.
To treat a praetorian in the camp, simply open Camp Management and place the praetorian in an infirmary slot. A praetorian cannot be used during this time. If the player wants to keep using the praetorian, the player can go back to the Triage tab and start treatment using a doctor. However, this will cost medicine.
Related: Is there a time limit for conquering territories in Expeditions: Rome?
A praetorian can only have one injury at a time. The Severity of an injury determines how close the character is to death. Risk describes how likely it is that an injury will get worse the longer it is left untreated.
Within the Triage tab, you’ll find Treatment Information, which tells you how long it will take to bring the character back to full health and how much medicine you need to purchase each day. A doctor is needed to treat injuries on the field. Players are assigned Syneros by default, who is a great healer.
For more information on Expeditions: Rome, check out What Commanders should I pick in Expeditions: Rome? and Can you save Gaius Julius Caesar in Expeditions: Rome? on Pro Game Guides.