Left knee joint pain. For long time.

Generally athletes get ligament tear, in common words sprain due to excessive rotational force which will cause pain if not healed properly. Since he can able to walk and withstand the weight of his body normally from past one month chances of having fracture is less, so its sprain which would have happened while you are playing, generally it takes 6-8 weeks time to heal but if he resume his athletic activities in between without taking rest, he will have pain again...Ensure that you maintain an appropriate posture while working or sitting or walking....Take frequent stretch breaks and drink lots of water...Discontinue using pillow while sleeping straight...Do not lift heavy objects, especially after bending down....Eat a healthy wholesome meal which should satisfy your minerals and proteins requirement...So consult a orhopedician for further management.