It's not patellar tendonitis, the pain isn't sharp or anywhere on the outside of the knee. The knee itself doesn't pain, just that the joint feels a little stiffness and a dull ache for a few hours after playing intense games of doubles and singles. I'd been playing for 6 months before this pain started, it started particularly when my game started moving from beginner/intermediate to intermediate/advanced and I incorporated more of the jumping lunges to the front corners. It goes away if I don't play for a couple of days. It's not a joint lubrication/arthritis problem, I've got that checked in the past. It's also not a major injury like a torn ligament. I personally feel that I'm doing something wrong in the way I lunge that's putting my entire bodyweight on the knee. I can feel it while lunging as well. I should be pushing my body forward and landing on the leg but I feel like I'm pushing my bodyweight downwards, adding extra pressure on the joint. One is supposed to have a "light" footwork in badminton, what would be some tips and exercises for me to improve that and hopefully alleviate my pain? Thanks!
What do you mean by a jumping lunge? The only times I think a person should jump would be for attacking a serve (jump forwards), or when incorporated in footwork into the rearcourt (china jump etc). There are many videos on youtube about footwork and practice. Tobias Wadenka probably has the best one. Make sure you are landing heel - toe, the foot is facing the direction of travel and the angle of the knee doesn't go less than 90 degrees.
I'm not sure if you have what I have, but after proper warmup + wearing a knee brace, most of the pain has gone away. Strengthening leg muscles by doing squats also helped for me.
