The 63-year-old former Liverpool manager met the media for the first time since being named as Martin O'Neill's replacement on Friday but will not be in charge for Monday's Premier League clash with Stoke City, Villa's website said.
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Houllier's first match in charge is likely to be the League Cup tie against Blackburn Rovers on September 22.
Kevin MacDonald, who has been managing team affairs since O'Neill's shock resignation on the eve of the new season, will remain in charge until Houllier begins his duties.
MacDonald has ruled out becoming Houllier's assistant and is expected to revert to his former post as reserve team coach.
"I am working on naming an assistant manager," Houllier told a news conference on Friday.
"Joint management doesn't work, but in some capacity as assistant manager he would have been helpful. He could also have maybe learnt the trade and, who knows, taken over from me.
"But I understand his decision, he's a nice bloke so I won't hurt him - I told him I'd like him to stay at the club."
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