So it proved as Souttar found himself on the steepest of learning curves against a star-studded Belgian side who ran riot in a 4-0 friendly win at Hampden.
McLeish kept faith with his central defensive protege who helped Scotland keep a clean sheet in his next appearance, a 2-0 UEFA Nations League win over Albania, before experiencing the disappointment of being sent off in a 2-1 defeat away to Israel in the same competition.
Souttar, of course, subsequently had to face setbacks of a more severe nature with the serious injury problems which meant he had to wait another three years for his fourth and most recent Scotland cap which saw him score and perform brilliantly in the memorable 2-0 win over Denmark at Hampden last November.
McLeish was at the national stadium last Saturday to witness another fine display from Souttar, albeit in defeat for Hearts in the Scottish Cup final against the Rangers side he will be joining next month under freedom of contract.
It was a reminder for McLeish of a particular quality which first attracted him to Souttar, one which resonated with a mantra he was familiar with in his own days as a top class central defender for Aberdeen under the most celebrated Scottish manager of them all.
“John played so well in the final,” said McLeish. “He’s a terrific passer of the ball and he likes to play out from the back.
“I remember Sir Alex Ferguson used to say ‘if you are going to pass, then mean it’. Souttar does that.
“He looks a suitable candidate to play in the Rangers back line.
“You have to have players lined up to take over because every year people move on and you have to be ready to go.
“I’m sure they will have other names in mind to bring in to strengthen them for next season.
“Souttar is already done and he’s coming in in the summer and I’m sure he will do well for the club.
“He’s at a good age, he’s a Scotland international and he’s a proven Premiership player.
“He’s had a few injury setbacks in his career but he’s got over them and hopefully that stays the case.
“I gave John his first senior cap and I’m delighted to see him growing over the last few years.
“He had to learn quickly at that level but he has grown since then.
“You get better the more you play at the top level for club and country and I hope that’s the same for John.”
It remains to be seen who Souttar will be playing alongside in the Rangers defence next season with both Connor Goldson and Leon Balogun out of contract next month.
McLeish believes the departure of Goldson would be an especially sore blow for his old club.
“Connor has been a terrific servant to Rangers,” he said.
“I’m sure there are players the club can bring in but it will be a shame to see him go if he does leave.
“He’s been at the heart of the defence for a good few years now and he’s been superb.”