When you encounter an injured motorcyclist, **you must not remove their helmet**. This is crucial to protect the injured person's neck and head. Moving the neck or head incorrectly can worsen injuries, especially if there is a cervical injury.

- **Keeping the helmet on** helps stabilize the neck and head, preventing sudden movements that could aggravate a possible spinal injury.
- If the injured person is conscious, it is important **not to move them** and to check for other injuries such as bleeding or fractures.
- If the injured person is unconscious, first check if they are breathing, but **without removing the helmet**.

In summary, the helmet acts as additional protection and its removal without the proper technique could be harmful. Therefore, the correct response is **not to remove the helmet**.