Hello good evening
The history you have given is very vague and less
Please answer the following questions
1) from when is the pain?
2) is there any history of trauma or fever?
3) do you loose balance which walking? Or is there locking of knee?
4) do you experience pain in any other joints?
Next Steps
Get an Xray first.
Both knees standing and then share the X-rays with me.
Until you get an Xray
1) avoid squatting, kneeling, cross legged sitting, Indian toilet, climbing stairs
2) physiotherapy
3) pain killers and anti inflammatory
4) local application of pain ointment/gel with hot water fomentation
Health Tips
Most of the times you being a tennis coach there are 2 common possibilities.
1) strain of both knees
2) chondromalacia patella- cartilage loss in the patella, increased wear and tear
3) meniscus injury
Consult an Orthopedic surgeon