Sheffield United's 1-0 defeat at Burnley on Monday night means Blues will again make an instant return to the top flight if they pick up three points against play-off hopefuls Preston.
Other permutations could also be enough as Blues look to match or better the results picked up by Sheffield United and possibly Cardiff, but with the midlands outfit playing in the 5.20pm kick-off they will know exactly what they need to do.
Birmingham are asking fans to turn St Andrew's into a sea of blue by wearing the club's colours and McLeish said: "I'd like to think there'll be a full St Andrew's crowd against Preston.
"The fans were brilliant against Wolves recently and if we get that support it will give the players extra energy.
"Hopefully St Andrew's will be rocking like it was against Mick McCarthy's side and we can go out there and put in an equally impressive display."