Harewood was part of an O'Neill-led Aston Villa side that finished sixth in the Premier League for two seasons running (plus a third while the now-retired striker was loaned out to Newcastle United).
But after the former Forest winger became the 13th City Ground manager in seven-and-a-half years last month, Harewood expressed to Talksport his concern that O'Neill will not get the time he needs to turn the club around.
"Martin is the man of the job," he insisted. "Obviously, he will need time. But [it depends] how much time he gets given, because the owners are are looking to go instant[ly] back into the Premier League, or into the play-offs or top spots. They are going in that direction it's just how quick[ly] they can do it."
Michael Gray, who played under O'Neill at Celtic, agreed with Harewood. But the Nottingham Forest academy product asked: "Do you think [O'Neill has] got time, though? Because of the owners, they want instant results.
"Forest, to be fair, they were the best footballing side I've seen for a long time, under Karanka.
"Now Martin has gone there they will obviously want results. Do you think they're going to get those results in a short space of time?"
Now 39, Harewood was a member of the Nottingham Forest side that last appeared in the Premier League, 20 years ago.
The Reds have been a Championship or equivalent club for 17 of those, having slipped to League One at one stage.
O'Neill has led Sunderland and the Republic of Ireland since leaving Aston Villa at the start of the decade.
Can the former Aston Villa manager get Nottingham Forest firing?
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