The 63-year-old Frenchman failed to win over the Villa fans during his relatively short stay in charge and, after suffering a recurrent heart problem, he was left with no choice but to leave the club.
“The doctors advised me to not resume before late in August or early in September, so it was a problem," said Houllier in an article in The Mirror.
“The officials were also scared my comeback could be postponed again at that time. I can understand that. The risk exists.
“They [Villa] are still traumatised with what happened last year, when Martin O’Neill left five days before the start of the season. So they didn’t want such a possibility to happen again."
Despite suffering from the serious heart condition the former Liverpool and Lyon manager has not ruled out a return to management one day.
“Coaching is my job, my life, my passion," he said.
"Maybe I will go on living in Birmingham for six months or one year, to have a good rest.
“I am in the countryside and very close to hospital and that is the perfect place.”