Harry Kane has a history of ankle injuries and when that is the case, it often results in a laxity in the ankle ligament caused by previous injuries.
Though he has never needed surgery due to an ankle injury, it's possible the laxity means the chance of turning the ankle is increased. Ligaments prevent excess movement and if there is too much laxity from previous injuries you get too much movement.
You never know the extent of the damage until the injury is scanned. That is an MRI scan and they might X-ray as well.