Sounds very like what happened to me around 25/07.
Except that mine was healing nicely, I turned to close a door and I felt a faint 'pop' from my leg.
Advice from the doc on this one:
Probably a tear, probably a smaller muscle which, if it goes completely, I don't need(!), (digitorum longus or tibialis posterior?). It's more likely to recur if I don't mobilise it right now. He reckoned it wouldn't be a 'fixed in two weeks' job though.
I've booked for the physio, but that's going to take a few days to come through and she's worse than the army type, temper-wise.