Is it permissible to inform a struggling worker that the money given to him as a debt was originally from zakat, especially after his delay in repayment and his injury at work, knowing that the intention from the beginning was to count it as zakat?

If the worker is poor and you request a loan, and you give him money with the intention of it being zakat (definition), then this is permissible, and the zakat is valid. It is appropriate to inform him that this money is his, without explicitly stating that it is zakat, in order to spare him embarrassment. There is no obligation to inform him that it is zakat, as it may break the poor person's heart. However, if he is eligible for zakat, it is not permissible to mislead him into thinking the money is a loan.