The former Wimbledon, Luton and Nottingham Forest boss was taken ill at the team hotel last weekend on the morning of the Magpies's' 3-2 victory at West Bromwich Albion.
Having remained in hospital over the weekend, Kinnear was expected to be discharged on Tuesday and be back in charge of the side in time for the clash with Everton on February 22.
However, the 62-year-old Irishman, who suffered a heart attack 10 years ago while in charge of Wimbledon, is now set for an extended period away from the game, possibly for the rest of the season.
Newcastle have confirmed they will not be making any statement about Kinnear's condition in the near future, with assistant Chris Hughton, who took charge of the side on Saturday in the manager's absence, expected to remain at the helm.
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