I thought about suggesting testing for pedal pulses but would they not be present in anycase as any DVT would be on the way back to the heart, thus past the place you would feel for a pulse?

MO isn't usually acutely painful to touch at this early stage and it is much more common in the quads than in a calf muscle. It is more of a laying down of calcium in the bone and beomce more of a hard non-extensile lump rather than a painful cyst (which this could be).

The ankle swelling I assume is unilateral - on the injured side only?

You might also consider a ganglionic cyst that could have resulted from the direct trauma. Are there any distal neurological disturbances?