Birmingham face United at Old Trafford on Saturday.
McLeish said: “I think it’s ominous, the fact that they’ve got to this stage unbeaten and their form is probably gathering momentum.
“They are probably looking better now than in the earlier part of the season when they had a lot of draws.
“It’s amazing that they are unbeaten and I think that they can only get better.”
McLeish added, when asked if United could go unbeaten through the season: “Of course they can. It would be a hell of an achievement.
“In terms of the title, it is such a tight league but Manchester United have so much experience of this situation.
“There is no man who has got greater experience than Sir Alex when it comes to the run-in, and the run of games after January.”
