Millwall will be sponsored by the national charity Prostate Cancer UK next season.
The Lions recently turned down an offer to be sponsored by pay-day lenders QuickQuid and have instead waived any fees, making the sponsorship free for the charity.
Millwall director Trevor Keyse and record goalscorer Neil Harris, now back on the coaching staff at The Den, have fought their own battles with male cancers and the club's fans have already helped raise upwards of ?70,000 for an appeal set up by Harris to help fight prostate and testicular cancers.
Lions chief executive Andy Ambler said: "A motto that we have adopted at our club is 'Football is the answer, not the problem'.
"There is so much that we do, and can do more of, which enables Millwall to be a force for good.
"We are a family club and like every family we know many close to us who have suffered the effects of cancer."