In a memo distributed to more than 2000 IMG staff worldwide, McCormack's children - all of whom work within IMG - said he remains in a critical condition and has yet to regain consciousness.
Authored by Breck, Todd and Leslie McCormack, the memo says their father remains in a critical condition in a New York hospital.
Said the memo: "His blood pressure and heart rhythm are stable though he has yet to regain consciousness. He has made progress over the past week and his doctors remain hopeful. However, a full recovery will certainly take time."
They went on to thank staff for messages of support and said all emails received were being read to their father in a bid to aid his recovery.
In his absence, Bob Kain, president of IMG's North and South American units, and Alastair Johnston, head of its international divisions, will oversee day-to-day operations of the firm.
McCormack suffered a heart attack on Thursday.
For a profile on McCormack, read the features section of sportbusiness.com
