From Arseblog this morning, things are not quite as they first appeared:
"According to the specialist who will operate on me it’s a small tendon that runs next to the achilles tendon and is irritating it, and it needs to be taken out. It is a small tendon that doesn’t do very much. Hopefully that will solve it."
It appears that this problem tendon may be the Plantaris tendon. It has been implicated in Achilled tendinopathy. It may also be related to another muscles' tendon, an accessory soleus muscle has been implicated as well! The more likely is plantaris and as you can see above, it is closely related to the Achilles.
Certainly this operation is less drastic than what I had initially envisaged. Maybe he can be back in six weeks if this cures his problem, the problem is that it might not and then the can of worms opens. Fingers crossed anyway.