Large fluid filled lump anterio medial aspect of shin

Hi. I need some advice. I woke up recently with a small lump on my shin which looked like a very deep blister (apparently filled with clear fluid). Over the next few days the lump became large and painful and led to ankle swelling/oedema (mild). There has been no bruising. The lump has slowly reduced to about 30% in size over three or four weeks having rested it as much as possible. Xray nad. MRI results awaited.

Approximately one month prior to the lump i had a mild injury during a football game at approximately the same spot. Shin to shin tackle. I continued to play and drove home and felt minor discomfort for a few days. My 2 year old then jumped on the same spot 2 weeks later leading to extreme sharp pain that quickly resolved (unless i really pressed on the same area). These might be related but the lump did not surface until 2 weeks later.

I normally cycle about 60 miles a week. I run occasionally but not recently. I have signed up for a marathon in 8 months time.

Any advice on possible diagnosis/treatment would be great.