You can't be disciplined for just being off sick unless it is discovered that the sickness was not genuine, or you did not follow company procedure about reporting your sickness. Even if the employer tried to claim that the sickness was not genuine, they would have to have a disciplinary hearing, which would by law involve you being informed about it taking place, and giving you the option to attend witha family member or union representative.
It is also likely that the company would have to seek some medical guidance on the condition that you reported as your sickness.
Q1, How long has the person in question been sick for? Greater that 3 Days?
Q2, Did the person report their sickness at the first possibility that they were able to? It is understtod by law that it can often be difficult for a person who is unwell to report this situation.