I'm no expert but I would most definitely contact the airline.
I'd guess you'll need a 'fit to fly' letter from your doctor.

Have you contacted your insurance company too?
I think most policies say that you need to tell them of any change in your health as soon as it happens.

Thanks Polly, I will let my son know.

jayjan,

Refer to Jet2's website, especially the bottom of the page.

Darren

I have read that dazbo and downloaded the pdf file for the medical form, but really this section is referring to someone with plaster cast on that cant bend their leg, so the information is a bit of a grey area, obviously he will be best ringing the Jet2 telephone number given for mobility & medical.

The difficulty with flying with a plaster cast, especially on a lower limb, is a higher risk of DVT due to the immobility. Most people suffer some degree of minor swelling due to both sitting down (gravity!), lack of movement and air pressure changes and in a plaster cast this is exacerbated!!
He must get a fitness to fly certificate from his GP or consultant and seek advice (NHS direct?) regarding the increased possibility of a thrombosis.
Some countries also insist that x-rays are carried (though I'm not up to date with which ones now!) as proof of the injury. Drug smugglers have been known to use casts as a sneaky method of importing illicit substances, so seek advice as to whether this applies also.

Thanks Tah will pass info onto my son