Hi and welcome
It looks like a burst cyst that may or may not be infected - without a hands-on examination that is impossible to decide. Please have it checked by a vet tomorrow.
What do I can’t get it check until next weekend?
Ok, thank you!It shouldn't wait that long if at all possible. Please keep it clean and wash it daily in saline solution, which you can either get from a pharmacy (the sterile version) or make at home by mixing 2 teaspoons of salt into 1 pint/500 ml of boiled, cooled water.
See a vet promptly if the cyst and the area around it starts looking angry and is hot to the touch; in this case you are dealing with an acute infection.