Thanks for posting your query.
It might be meniscal injury
.These occur with tibial (shin bone) rotation while the knee is partially flexed during weight bearing (football, soccer, ski, etc.).
I suggest you to consult an orthopaedician nearby for a detailed examination. You may get the X-ray of the area affected under his/her guidance to rule out any bony injury.
In the interim, ice the affected area and take anti-inflammatory drug like mortin to reduce pain and inflammation. Avoid putting weight and rest well.
Dr Saurabh Gupta