Kneecap more red on one side and thigh thinner than opposite side

Hello,

I have noticed in recent months what feels like a weaker left leg than normal. I had been noting my knee sore before and after exercise.
I have noticed that my left thigh is thinner than the right. It is very visible both directly above the knee and mid thigh, where it seems I have 20 inches on the left but 21 inches on the right. The left kneecap gets quite pink/red when exercising and at rest less red/pink but still different toi the right side which is normal.
I have a regular routine of walks several times a week. twice a week I will
do 3 miles over the malverns. It involves a 1000 feet climb in 26 minutes or so. Otherwise I do walks 3 to 4 miles on the flat and in the better weather (spring/summer/autumn ) I will cycle one hour to one and half
fairly hilly.

Given this routine I would expect to have well developed muscles in 'reasonable' but not perfect symmetry. I do have fairly severe cervical disk disease with narrowing of the exit foramen but not so far
pressuree on the spinal cord.

I have visited myt GP who carried out a fairly thorough examination involving examinatioon of patella and testing of knee strength and straight leg raises etc. The knee wasnt so red when I saw him as I had been resting and went to an early appointm,ent but he suggested it is not significant

The kneecap on the affected side feels distinctively cold at rest and there is very much less hair on that side, all of which which to me suggests poor blood flow

He did noty offer a explanation for my symptoms, or a potential diagnosis , but recommended some chair based leg raises and some
wall sqauts

Any suggestions ?? Especially as regards the red /pink knee on one side and the muscle weakness which amounts to about 1 inch circumference.

I have often found that knee to be niggly over the years, wioth episodes of deblitating soreness and it was why I have up running over 10 years ago

I hope someone can advise