Welcome to HealthcareMagic forum.
You seem to most probably have a superficial bruise
rather than any deep musculoskeletal injury
will help to resolve pain and swelling caused by the inflammation .
Most bruises would resolve significantly over 2-3 weeks. Yes there is a risk of a blood clot arising from surgery or injuries to block blood vessels in limbs
, brain , lungs etc during long flights but the risk is more in deep tissue / bony injuries and surgeries. As in your case it's just a 6 hour flight and the injury seems superficial such complication is less likely . Also you can prevent it by avoiding prolonged sitting or frequently moving limbs or changing posture to ensure proper blood circulation of legs .
So please go ahead with your journey however if your swelling does not decrease in a weeks time do consult your doctor for reevaluation and management .
Wishing you good health.