Hello and welcome to the forum. I would imagine your doctor will make the best choice in what to use for your ACL reconstruction but the gracilis tendons are often used for grafts. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3435898/ This article discusses different graft choices. When is your surgery scheduled for?
Here is general information on the ACL reconstruction surgery. https://www.mayoclinic.org/tests-procedures/acl-reconstruction/about/pac-20384598
What precipitated the need for the surgery? Did you have a sports injury?
Have you consulted again with your doctor? Decided on what type of surgery, which choice of graft to do?