In reply to KlaasW:
I'm no expert, but for various reasons my better half has researched this to death.
If it is the peroneus longus you will be able to get away with it for a short time. Take ibuprofen, ice the area with peas/ice/chilled stuff in a towel, and consider some lengthways taping or a compression sock to keep down the swelling. Bouldering is likely to make it feel sore.
In the longer term, you really should go an get this properly looked at. Damage and ruptures to the PL are often poorly diagnosed. In some cases, there can be a complete rupture with little consequence. In other cases even minor damage can have fairly significant consequences. Push to see someone who really knows what they're talking about, ideally a lower limb specialist (not a surgeon) with sports med experience.
Good job it's a trip to font and not a hiking trip!
Good luck getting it sorted.