Forest currently sit third in the Championship table, with an incredible 16-match unbeaten run helping to fire them into the second tier promotion race.
They will fancy their chances of causing a cup upset when Birmingham head to the City Ground on Saturday, and McLeish is all too aware of the Reds' credentials.
Having worked with Billy Davies when he was still a player at Motherwell, the Blues boss insists he always knew that the fiery Scot would one day become a competent coach himself, and knows he will not be able to underestimate his in-form Forest side.
"I could definitely see Billy going into coaching," said McLeish.
"He had his own amateur team, which he ran and was a big student of the coaching side.
"Billy has coached Forest well and got them playing with his winning mentality.
"I tipped Forest at the start of the season to be a surprise contender for promotion and we have probably got the hardest tie of the round.
"He has a mobile team and I have watched them in the last few games. Billy has built a cracking little team."
Nottm. Forest v Birmingham Correct Score: Nottm. Forest 2-1 9/1