There’s a poster who is, I think, a physio which gave a fairly good summary somewhere (might even be this thread if I could be bothered to look!) but my layman’s understanding of it is that it is inflammation (...itis) of the fascia which is a membrane surrounding muscles. When you take the skin off a chicken breast the thin membrane underneath is the fascia, when this is damaged or inflamed (the plantar bit is the bottom of the foot) it can ‘snag’ on the surrounding muscle etc. “Myofascial release” is what a personal trainer taught me to do for that issue, with the foot you can roll a tennis ball around under the sole to help, but I imagine a pro sportsman will have some hands-on from the medical team. I think it can be one of those niggly ones, sometimes goes away reasonably quickly, but can take longer. So I’m not sure if they will know for sure how long.
Apologies if I’m repeating anything (haven’t read the whole thread) or if my limited knowledge is incorrect, but that’s my understanding of it.