Lame yearling

[Vikki89]

went to yard this morning to find my yearling is lame. he has scabs on the back of he knee which are quite sore. Thought it could be mud fever but am wondering if it could be something else.
Has anyone got any ideas on what else it might be?

 

[PapaFrita]

My money's on hoof abscess. Could also be mudfever but as I understand it it doesn't usually cause lameness.... (I might be wrong though!)