to be perfectly honest, the way you have described it sounds like you are making a mountain out of a molehill. Do you want to leave? is someone questioning why you are off sick really something to hand your notice in over? Cant you just speak to the person concerned and say you feel disappointed at his comments and can you both let it lie now? I dont know much about employment law but i would have thought that anyone looking from a constructive dsmissal angle would wonder why the hell you left over something that seems so trivial (i know it dosent seem trivial to you, but give it a few days and it might)
Hav you another agenda you havent told us about? Do you want to leave? If this had never happened, would you be thinking about leaving?
your manager sounds a bit crap really, as it could have been very vry easily sorted by him/her saying 1) roonaldo has a prior arrangement about hours that is none of your business and b) an employee being off sick is something for me to worry about not you