If you have been suspended, it should be on full pay. Agree with others, it's a pathetic way to treat an employee just come back to work. It cannot be demanded that you utilise your own holiday because of this.
Contact HR department if your company is of a size that they have specialist HR people. They should understand the situation better. They need to come up with a proper assessment of the work that they could get you to do, given the limitations. It should also be determined in the light of the prognosis of whether this is for the long-term, or whether you just need light duties to get you started back into work for say the next 2 months.
If this really is a long-term problem for you, and they really, really really want to claim that you are now unemployable (and this would be really unusual) the process they would have to go through would be to dismiss you on grounds of capability. That is one of the 'fair' (in a legal reasons) for dismissal, but they have to follow a process - or face the possibility that you take them to an Employment Tribunal for unfair dismissal.
(I stress that I am merely explaining the worst case scenario for you. I assume that you have at least 12 months continuous service??)