Step 1: We need the statement that does not hold true. Management of a haematoma is individualized to its size, site, and symptoms.
Step 2: Imaging like MRI genuinely assesses the bleed and the GCS genuinely guides prognosis, so those two are valid statements.
Step 3: The claim that every haematoma must be operated is incorrect, because asymptomatic or small collections are simply observed and many superficial bruises are handled conservatively with the RICE approach.
Step 4: Surgical drainage is reserved for selected symptomatic or critically located haematomas, not for all. Therefore the false statement is that a haematoma must always be operated.
\[\boxed{\text{Haematoma must be operated}}\]