I would presume the person didn't diagnose a blood clot as often blood clots cause a purple colour to emerge where the clot is.
If it was a clot they are a mixture of platelets and fibrin. The same two things that cause scabs. Platelets form the sticky lower layer and the fibrin, a blood protein, creates a mesh like layer out of things called fibrils and these two things cause a clot, but as the fibrin is a blood protein getting rid of clots can be done with a protease, a protein digesting enzyme, one such enzyme I've heard of in conjunction to clot dispersal is plasmin, as it breaks down the fibrin, leaving just platelets.
Clots could be a thrombus which are static clots, or an embolism where the clot starts off somewhere else and is shunted around the body and settles elsewhere.
Obviously I have no idea what is bothering you YAH, but if it's not a clot then it's a possibility it is a nervous problem of some kind, as were it a muscular problem, some muscle problems have severe bruising attached, if the muscle is torn, but if it is strained then maybe no bruising has shown, although sometimes injuries that can cause inflammation don't and inflammation encourages healing processes, so some people undergo something called the Graston technique to encourage the inflammation.
As it's a leg it could mean it's a problem with the piriformis, obturator internus, inferior or superior gamellus tendons that connect to the hip joint, or it could be the posterior cruciate, anterior cruciate or lateral or medial collegiates, or a patella tendon issue, but those last five things would affect knee mobility and / or knee joint stability, as would the meniscii, were it the medial or lateral meniscus being strained or torn in some way.
If it is a cartilage issue, it might be early stage osteoarthritis, unless it's just a bit of damage to the cartilage and not cartilage wearing away.
If you had any bursitis in the hip, inflammation of any hip bursa that might be it.
If you have done a lot of running and you have knee pain coupled with a grating sensation, it could be Patelofemoral syndrome a.k.a housemaids knee, a.k.a, secreteries knee, a.k.a runners knee, a.k.a chondro malacia patellae, which is Greek as chondro relates to cartilage and malacia refers to softening or degradation and this can occur through excessive running or cardio effects around the knee, or by sitting with the backs of the knees often in an acute position, known as the theatre position, because some theatres have the backs of seats too close to the knees of the people behind, so therefore if someone has a job that often requires a tight and tense knee position, like some secretaries for example, or kneeling a lot like a housemaid used to to clean floors, this could exacerbate the risk of PFS and one or two people on here in the past have had PFS and rest of the legs from strenuous use, NSAIDS and strengthening exercises for the quads and hamstrings, could possibly help to alleviate this issue.
The problem can create a grating sound and it results from cartilage being allowed to slip towards the lateral, outside, edge of the knee.
Some of the above suggestions might relate to your situation, but these are just some possibilities for your concerns, as I am using self education for these assumptions, not knowledge based on qualifications which I must stress.
I hope you get this issues sorted soon.
GOOD LUCK and please do keep us updated and try not to let these things affect you too much and if you can do any kin of exercise at all, try to do that for your own well being and sanity

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