Moreau, 25, a New Orleans native who had a Saints physical, announced his retirement in a tweet.
Moreau discovered Hodgkin's Lymphoma during a physical and will leave football to fight cancer.
Former Raiders player, drafted in 2019, visited Saints and Bengals before becoming a free agent.
During Moreau's examination, Saints team physician John Amoss diagnosed his cancer and aortic aneurysm.
According to NFL.com and the American Cancer Society, Hodgkin's Lymphoma victims survive 89%.
Moreau had 91 catches, 1,107 yards, and 12 TDs for Raiders. Career-highs in 2022: 33 catches, 420 yards.
Hodgkin's Lymphoma affects the immune system, begins in white blood cells, and is rarer than non-Hodgkin.
David Carr, Moreau's former Raiders colleague and current Saints quarterback, tweeted support.
Moreau is thankful for support and guidance from hundreds of people as he fights cancer.