Mr Law said: "The people of Glasgow need a 21st-century hospice facility and I would encourage everyone in the city to get involved with fundraising for this excellent cause.
"I'm very proud to have been asked to speak at the Prince and Princess of Wales Hospice Sporting Lunch and to be able to support the hospice."
Law is best known for his 11 years playing for Manchester United, scoring 237 goals in 404 games. He was named European footballer of the year in 1964, the only Scottish player to have won the award.
Morag Cunningham from the hospice said: "We are very humbled by the fantastic response to our annual sporting lunch. The hospice has many loyal supporters from the sporting world and it is fantastic that so many of them will be attending today.
"Having Denis as our guest speaker will certainly be a highlight of the day and his support of the Brick By Brick appeal is greatly appreciated by everyone at the Prince and Princess of Wales Hospice."