The London borough could be dominated by the multinational UnitedHealth Europe (UHE) within a year, he said.
Camden and Islington, City and Hackney and Haringey PCTs are seeking bids to run an out-of-hours service from October.
The move is seen as a fresh threat to traditional general practice in an area where contracts for three GP practices were awarded to UHE and where the capital's first polyclinic is being developed.
Current out-of-hours provider Camidoc's contract expired on April 1, but the company has been given a temporary six-month reprieve.
UHE earlier this year beat local GPs to run three Camden practices, including the Brunswick Medical Centre. A GP-led bid scored higher on services offered but not value for money.
A protest was held by patients and GPs from the area outside the DoH building in Whitehall on Monday.
A new GP-led health centre at University College London Hospital would handle all acute care except 999 responses, and Dr Glackin is concerned UHE is interested in that too.
UHE would not comment on the tenders.