I’ve had some issues with my knee feeling stiff while playing badminton, and have noticed that it can get a bit sore after longer runs, particularly on pavement. However, I’d been managing that by trying to minimise time on concrete, and stretching before and after a run.
What I didn’t realise was that walking 5 odd miles from Battersea Power Station to Putney along the river in my walking boots would make my knee stiffer than ever, and because I didn’t realise, I didn’t stretch afterwards.
Upshot is, rest from running for the next couple of days, and into the pool. I could go out on my new bike, but I need shoes and cleats etc. first.