Young is at the centre of controversy over the penalty he won against QPR last week.
Asked whether he would be especially mindful about Young, McLeish said: "We know that over the years players are clever and there have probably been a few disputed penalties since time began.
"But I don't really think there are a lot of divers in the British game. I know when I was in the Scotland job the SFA were really anxious to stamp that sort of thing out but it's so difficult for refs.
"It's a split-second decision when there is a little bit of closeness between players. Even sometimes when a player is going at full rate, the slightest touch can be enough to make him go down.
"Sometimes you make a decision that is wrong even from that point of view. But I don't envy referees at all. They have got a horrendously difficult job, in my eyes."
The beleaguered Villa chief, whose side sit just six points off the Barclays Premier League's bottom three, wants his players to be careful but not over-cautious when defending against the reigning champions.
"We'll try and stay on our feet against United's players at the weekend," he said. "Sometimes it's not as simple as that. You guide them and coach them to try to do that but at the same time you have to make sliding tackles and fair tackles when it matters.
"Maybe at the other end I'll be looking for more action from our lads."