Hleb is currently on loan from Barcelona until the end of the season, but McLeish insists the Belarus international can still earn a permanent move to St Andrews.
“Everybody knows what Alex can do when he’s at the right level,” McLeish told the Daily Star.
“It’s not crunch time for him – he still has plenty of time to impress.
“But there’s no point talking about what might happen next season.
“If Alex can produce some of his magic in one game then he can be worth his weight in gold now.”