The 71-year-old, who retired from management at the end of last season, helped dig the first square mile for foundations of a new wing for the palliative care centre this week.
The hospice, which is situated next to Hairmyres Hospital, cares for patients suffering from serious illnesses, including cancer.
"It is a fantastic benefit to the hospice to have such a public figure like Sir Alex take the time out of his busy schedule to come and give us support," the Daily Mail quotes hospice chairman Dennis Gallagher as saying.
"It lets people see the importance of this project to the people of South Lanarkshire, the fact that someone like Sir Alex can support us."
The new wing is expected to take 12 months to build.