Is there any danger to running/cycling with a thigh hematoma?

It depends: If you have swelling but have full range of motion without pain then you may be okay. If you are trying to cycle through pain due to the hematoma, the local trauma and bleeding into the muscle may get worse and delay full recovery or increase risk of "myositis ossificans, " which can lead to prolonged pain and stiffness and also prolong recovery.

Yes.: A thigh hematoma should be evaluated by a sports medicine trained physician. These can potentially scar and harden, forming a calcification within the thigh, that can result in chronic pain and dysfunction of the leg. Running/cycling can aggravate the condition, if not cleared first, by a qualified physician.