Got in my 2003 GMC Serria Exteneded Cad truck Saturday morning and heard a bad knocking as if no oil, checked?

Got in my 2003 GMC Serria Exteneded Cad truck Saturday morning and heard a bad knocking as if no oil, checked oil about a quart low,put in oil and ran as usual. Got in this morning to drive to work and knocking was as bad as every. Oil pressure betwee 40-60. Am I in trouble