Adding A New Item In The Sprint Backlog While The Sprint Is ‘Running’

I wanted to know if while developing a task during the sprint I discover that a new user story is required to complete the particular task, i.e. a new user story is required to be developed before I can complete an existing task, can I automatically add the new story to the sprint backlog? Or should I discuss it with the PO? If I don't complete the task, the sprint goal remains unfulfilled. And I cannot complete the task unless and until a new story is added to the sprint backlog and developed first.

Posted By - Prakash