Bannan has not been chosen for Villa's last two matches against Sunderland - for which he was suspended while the club held an internal inquiry - and Norwich.
When asked if a player could behave in the manner of Bannan, McLeish said: "No, not in this day and age. Listen, nobody's going to be too upset if a player has a beer - but at the right times. In the Premier League this is top-level stuff and you have to be absolutely right physically, and it's a wake-up call for every player, every young player."
He added: "I hate to talk to modern players about 'in our day' and say 'we did this, we did that'. It's just changing generations and you have to adapt to the times.
"It's probably not the right time to have a big debate about it. Barry is available for selection as he was for the Norwich game.
"I'm sure lessons have been learned. He's training really hard and actually looking really impressive in training and has the potential to reach the top level.
"We've had loads of one-to-ones, we've had talks with the whole group. We know how we want to go forward."
Bannan was also left out of the Scotland squad while the subject of a police investigation before being formally charged.
McLeish said: "I'm sure all these things hurt, like getting left out of the Scotland squad.
"But life's a big challenge and it's about how you deal with the next episode."