Is Popliteal Cyst On Knee Dangerous?

helo my daughter is 12 she fell over at school on her knee , i took her for a xray and they found a cyst in her bone area around the knee and told me to go to my gp in 2 months , for another xray , should i follow up sooner , than that and i thinck the nurse said it was popliteal cyst what are the dangers , with this cyst , can you give me some advice please.