The Sum 41 rocker shocked fans on Friday (16May14) by revealing his liver and kidneys had collapsed following years of heavy drinking.
Lavigne has since pledged her support for Whibley via Twitter.com.
Taking to the website on Saturday (17May14), she wrote, "Spoke to @Sum41 Deryck today. I am so proud of him. He is family to me and always will be. #StayStrongDeryck."
Whibley, who has been warned that one more taste of alcohol could kill him, was photographed for the first time since his big reveal on Monday (19May14). He looked extremely frail and thin as he was helped to walk around a Los Angeles neighbourhood by his fiancee Jocelyn Aguilar and a friend.
Lavigne was married to Whibley for four years before their divorce in 2010. She is now wed to Nickelback frontman Chad Kroeger after tying the knot last year (13).