Thanks for getting back to me. The issue here is that if you have been continuously employed at your place of work for less than 2 years then your employment rights will unfortunately be somewhat limited. Most importantly, you will not be protected against unfair dismissal or constructive dismissal. This means that your employer can dismiss you or force you to resign for more or less any reason, and without following a fair procedure, as long as their decision is not based on discriminatory grounds (i.e. because of gender, race, religion, age, a disability, sexual orientation, etc.) or because you were trying to assert any of your statutory rights (e.g. requesting maternity/paternity leave, etc.).
So even if you were being picked on because of your absence due to rehab, that is not a discriminatory reason and as unfair as it seems, it would not be unlawful (or more precisely you would not be able to challenge it legally). Of course you can still pursue it internally, such as through the grievance procedure but if that does not work and if you are eventually forced out or dismissed, due to your length of service you would not be able to challenge this.
I'm sorry if this is not necessarily the answer you were hoping for, however I do have a duty to be honest and explain the law as it actually stands. This does mean delivering bad news from time to time. I hope you understand and would be happy to provide any further clarification if needed. If you are still satisfied with the level of service you have received I would be grateful if you could please take a second to leave a positive rating by selecting 3, 4 or 5 starts at the top of the page. Thank you