The striker has joined Championship leaders Wolves on loan until the end of the season after struggling to make an impact at Villa Park.
He has started just one Premier League game for O'Neill's men since his 2007 move from West Ham United and has featured only twice since the turn of the year.
However, despite acknowledging his disappointment at a lack of opportunities, Harewood does not hold a grudge against his manager.
"It is frustrating when you're not playing, but Villa have been doing so well this year it's just nice to be part of that really," Harewood told Sky Sports News.
"At the end of the day, it's up to the gaffer who he picks at that time when the games come up, and now I've just got an opportunity to go and do well with Wolves."
Meanwhile, Wolves' chief executive Jez Moxey is confident Mick McCarthy is happy with the pre-deadline signings of Harewood and goalkeeper Graham Stack.
Moxey told the club's official website: "We asked ourselves if there was anything else we needed to do before the deadline closed and we are happy with the business we've completed.
"Marlon's signing was something Mick was very keen to do when we became aware of his availability and we're now relieved to be back to three goalkeepers after Darren Ward's injury problems.
"Mick was always very comfortable with his squad, but this is such an important run-in we wanted to make sure we had all bases covered and I think we have done that."