Joe Hart's withdrawal through injury means Foster, who replaced him between the posts at St. Andrew's this season, is favourite to start his first international for 12 months against France on Wednesday night.
He played successive internationals against Belarus at Wembley and then Brazil in Doha last season.
McLeish believes Foster is reaping the benefit of playing regular first team football after his lack of action at Manchester United before his £6 million summer move.
But he also gives credit to Blues goalkeeping coach Dave Watson, the former England Under-21 keeper, who worked closely with Hart when on loan from Manchester City - and now Foster.
McLeish said: "I think Ben just needed games and he is looking every inch a top-class keeper.
"At the end of the day, a keeper makes a mistake and it is normally a goal.
"That is the pressures they are under and must face and someday they will make a mistake.
"But the top ones make very few, that's the key, to a great keeper, and Ben has been excellent this season.
"Ben has been very, very solid for us in everything he's done - his taking of crosses, his distribution, his communication.
"It's all been there and you can see he's had a good grounding and been educated in a highly technical world.
"Sir Alex Ferguson, when he sold Ben to me in the summer, did say he would be vying for the England position by the end of the year."
McLeish added: "I'm also fortunate to have a good goalkeeping coach in Dave Watson. We look at everything together.
"Over my years in the game, I was the worst critic of my goalkeepers when I played for 18 years at Aberdeen and Scotland.
"I used to get frustrated with the keepers but Dave is doing a great job."