Redknapp, 70, has taken over from Gianfranco Zola with the club fifth from bottom in the Championship, just three points off the bottom three and facing Midlands rivals Aston Villa on Sunday.
Redknapp should have been managing a jockey’s side for The Injured Jockeys Fund at Cheltenham on that same day.
Instead, he will begin the task of keeping Birmingham in the second tier of English football and he knows it is not going to be easy.
“You could put Fergie in the same position and he’s not going to suddenly come in and make these players play like Manchester United,” said Redknapp.
“Players don’t need telling they are rubbish – they need to be given some sort of confidence.
Harry Redknapp believes even Sir Alex Ferguson would find it tough to give Birmingham a quick-fix
“My philosophy is players will respond more to a pat on the back than being slated. It’s confidence that you need. Sometimes you just have to run around a bit more as a player.
“There’s nothing clever about that. If you stand around then it’s no good to anyone.”
Birmingham were seventh Zola replaced Gary Rowett but the new manager won only two league games in 22 before resigning after Monday’s 2-0 defeat at home to Burton.
Now the challenge falls to Redknapp but the lure of the game could not keep him away.
“I could easily have said goodbye to it all but I love it. I am just a mad football fan,” said Redknapp.
“The lows of losing against Aston Villa on Sunday will be horrendous but if we win I will be singing in the car all the way home.
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“That’s the way it is. You go home after losing and it kills you. But if you stop caring then it’s time to get out.
“I had promised to manage a side for Tony McCoy for the jockeys’ fund which is a great charity but I can’t do that now.
“Funny really, because I was a bit worried about that because I didn’t know any of the players – a bit like here really.
“I was worried how I was going to find a centre half among the jockeys with them all being so small. Now I’ve got a slightly bigger problem.”
The former Tottenham manager has agreed to take over until the end of the season and it is all so new to him.
Redknapp takes over from Gianfranco Zola with Birmingham fifth from bottom
He said: “Birmingham are a team I’ve not see much of, seen nothing of really, they’ve not been on TV much this year.
“I am a bit like that, I tend to dive in. It was something I thought ‘I’ll have a go at that’.”
Blues have not won for nine matches, with their last victory a 2-1 triumph at Wolves on February 27 and Redknapp heads into the game after his most recent job was coaching a local Under-10s team.
He said: “I went over the park two weeks ago and coached some under 10s. A guy came and did a bit of work at my house and started telling me how he coaches his little boys’ team and would I come over?
“I did two-and-a-half hours, Saturday and Sunday morning. I love it. While I’m still fit enough to do it and wanted I’ll always pop up somewhere.
“Villa’s a tough game to start with, a local derby and it will be great atmosphere. I am sure Steve Bruce will do a good job in the long run but Birmingham’s a big club too and should be pushing for Premier League.”