BBC Radio 5 live's Pat Murphy said: "The decision will be in the interests of Aston Villa, not Houllier.
"The delay may be over severance pay. Houllier still has two years left on a contract worth more than £2m a year."
Murphy added: "Houllier and his management team have remained bullish about his prospects of returning to work but a final round of medical tests late last week would have taken the decision out of Houllier's hands."
Medical test results have been studied by the club's owner Randy Lerner and medical staff. Houllier missed the final month of last season because of his heart problems.
