The Minnesota Vikings legend announced the news on his Instagram page Friday afternoon ... telling his 640,000-plus followers that he's been in the hospital for the last six days dealing with surgery related to the disease.

Moss appeared on camera to give his fans the update -- and he needed a cane to move in front of the lens. The 47-year-old was, nonetheless, in great spirits -- as he wore a grey, lavender and black "Team Moss" shirt that read "Let's Moss Cancer."

Randy shared that doctors recently discovered a cancerous mass "in the bile duct right between the pancreas and the liver" after he noticed some discoloring in his urine.

He stated he first had a procedure to deal with the issue on Thanksgiving -- before he went on to have a bigger surgery this week to remove the growth.

"They found it and got it," Moss said.

While the Hall of Famer described himself in the vid as a "cancer survivor" -- he did say he still will have to go through "some chemo and radiation."

Moss thanked all of his family, friends, supporters and "prayer warriors" -- and he urged everyone to go to RandyMoss.com and buy his Team Moss merch, as some of the proceeds will go to helping the fight against cancer.