Haener made the announcement during a press conference at Saints training camp.
A reporter asked Haener about a bandage on his face, asking if it was a "battle wound," when Haener announced the diagnosis.
Haener said he is working with the team's training staff and has a consultation on August 1 to discuss the next steps.
He clarified that the cancer is not considered to be life-threatening.
He said family members grew concerned when a bump on his face continued to grow right before training camp started.
EDITOR'S NOTE: The video above is from a previous broadcast and will be updated.
The bump was removed and a biopsy was done to confirm the cancer.
Haener said he is doing well mentally and is relying on the medical staff to help him going forward.
He was asked about the name of the cancer but said he is keeping it private with himself and the organization.
Haener was drafted by the Saints in the 4th round of the 2023 NFL Draft.
Haener's career at Fresno State ended in a 20-5 record as a starting quarterback, a completion percentage of 68.2 (1st in Fresno State History), 9,120 passing yards and 731 pass completions (4th), and 67 total touchdowns (5th).