Deduction for medical costs to speed up return to work

Have a client who runs a ski school, and as such employs professional skiers as teachers.   One of their most popular employees (has a large number of clients who specifically hire him personally, rather than his employer) has suffered an injury which prevents him from skiing and so currently cannot carry out his job until he has an operation to repair the damage.

It would be possible for him to get his injury treated on the NHS, but the waiting lists would mean that it would be some time before he would be able to return to work.  Instead by opting for private medical treatment he could return to his job much quicker.

Are there any grounds for treating the costs as truly deductible - and not just deductible for the company but then taxable on the instructor himself as a BIK?  Struggling to get beyond HMRC's wholly and exclusive rules.

Any pointers would be much appreciated.