It was actually to subsidise his income for the period he would be out of action.
from the gofundme: Originally this crowdfunder was to provide some income for Callum to help him and his young family get through a year out of football, but we have today been told that while the PFA are kindly funding 50% of the costs, he needs to find the other 50% of the cost by Friday 17th March or the operation will have to be delayed, and even after the operation, he then faces 9-12 months of rehabilitation.
To me it seems to be a bit odd, as he is either supported by the club as an employee (and their insurance) or he claims from the welfare state.