McLeish has confirmed McTominay will be in his squad for friendlies against Costa Rica and Hungary later this month.
The Lancaster-born midfielder qualifies for Scotland through his father and rejected the chance of an England Under-21 call-up after meeting McLeish last week.
• READ MORE - Scott McTominay pledges allegiance to Scotland
When asked on Sky Sports News HQ whether McTominay would be named in his squad, McLeish said: “He will be, I don’t think that’s the world’s best-kept secret.
“Scott was very receptive. I looked him in the eye and he gave me a passion about playing for Scotland. I saw the passion and I really felt that we had nailed it that day.
“Of course he has to play in a competitive game but if we can get him playing in the friendlies and he sees what it’s all about and we can have some good performances, obviously winning is the big thing, and then Scott will be very much a part of it.
“He has had some great games with Jose Mourinho’s Manchester United in recent times. The Crystal Palace game was a tough one for him but he is only 21, he has not got all the answers.
“I am 59, I think at my last count, and I have not got all the answers. But hopefully I will get more right than I get wrong.”
Scotland host Costa Rica at Hampden on March 23 before playing in Budapest four days later. McLeish names his squad on Monday.
• READ MORE - Jose Mourinho steered Scott McTominay towards Scotland, says Craig Brown