The reserves coach will relinquish control of the first team after Saturday's home match against Bolton.
Houllier will be at that game but as he has had prior commitments with the French Football Federation this week he has already asked MacDonald to prepare and select the team.
It is likely to be MacDonald's last involvement and although he is returning to the reserves he wants to take a step back to assess what the future may hold for him.
"I put myself up for the job and once I did that I knew there might be disappointment," he said after Villa's late 2-1 defeat at Stoke last night.
"It took me long enough to decide and once I didn't get the job I was very disappointed.
"But the decision to go back and work with the reserves when Mr Houllier came in was totally down to me wanting to re-evaluate and see what I can - or want - to do.
"I may need to re-think what I may want to do. I may want to be a manager.
"Some people might think I will make a good manager, some people might not - but I need to know for myself.
"Maybe I've gained a bit of confidence (as a result of his managerial duties) but I can't say it's changed me in any way."
MacDonald admitted there was never any realistic chance of him becoming Houllier's number two once the top job had passed him by.
The Frenchman approached Phil Thompson, his assistant when he was manager at Liverpool, only to be turned down and he has now made an approach for one of his former players at Anfield, Gary McAllister - currently assistant at Middlesbrough.
"I had always thought that when I did not get the (manager's) job that I wasn't going to do it (assistant).
"I think Mr Houllier is already in the process of getting some of his backroom staff.
"But if I am asked to do something by the Villa manager that is what I do because I work for Aston Villa football club, I work for Aston Villa's manager.
"He asked me on Friday if I would do those things (prepare the team for Stoke and Bolton) and I have no problem at all.
"That will still happen when I go back to the reserves. If he asks me to go out scouting I'll do some scouting, if he asks me to go and help with the first team I'll help out - until I decide what I want to do."
MacDonald believes he will hand over the squad in good shape having done a reasonable job in filling the breach when Martin O'Neill walked out on the eve of the season.
Had his side not conceded an injury-time goal to Robert Huth at the Britannia Stadium last night then the only blot on his Premier League record would have been the 6-0 drubbing at Newcastle.
But two wins and two defeats is not the worst start to a season and MacDonald is confident things will pick up.
"They are a good side, good players and there are a couple to come back in yet," he said.
"There is a lot for people to look forward to at Aston Villa.
"The performance last night was pretty good and some of the training has been outstanding.
"But the most important thing in the Premier League is to win, it is not about playing the football we are trying to play."
Having held Stoke at bay Stewart Downing's diving header in the 35th minute had given Villa the lead at the Britannia.
However, £8million club-record striker Kenwyne Jones headed in the equaliser 10 minutes from time before Huth's late intervention.