I would strongly recommend your line managers did not push for this. If required, your HR team may follow up in special cases but what help is it to your line manager if they get a complex medical assessment of a specific employee? Are they medically trained to be able to understand and interpret this information? Would this not just negatively impact the relationship the employee has with your organisation?
Focus on the adjustment not the medical condition.
It may be helpful for your employee to be referred for an occupational health assessment to gain an initial understanding of what workplace adjustments might be useful for them.
The vast majority of adjustment requests cost very little, if anything at all. Let’s not forget that there is government support available to support your employees with adjustments too in the form of Access To Work.