The 44-year-old former Anfield coach and Stockport manager has been diagnosed with non-Hodgkin’s lymphoma.
Ablett was taken ill last week, soon after agreeing a one-year coaching contract with Ipswich.
He had been due to sit alongside manager Roy Keane on the Portman Road bench for the first time in Saturday’s friendly with West Ham.
A sombre Keane, who recruited Ablett after getting to know him on a coaching course, said after the game: “Gary was taken ill at the training ground and taken to hospital. He is getting the best of treatment.”
Ablett’s family rushed to his bedside. It is expected he will be moved from Suffolk to his native Merseyside this week where intensive treatment will continue. The defender spent nine years at Liverpool from 1983 – where he won two league titles – before joining Everton.
Ablett went on to finish his playing career at Birmingham, Blackpool and Wycombe.
Keane’s squad went into Saturday’s friendly with the Hammers well aware of the seriousness of Ablett’s illness.