Jonathan Barnett admitted that Bale has endued 'a rough time under Mourinho' before the Portuguese manager was sacked last month.
"As I said to Spurs at the beginning: 'If you give him a run, put your trust in him, let him play his own game, not tell him he's got to do this and that, treat him like a [Lionel] Messi or a [Cristiano] Ronaldo' - I'm not saying he's as good - 'and you'll see'," he told SNTV.
"It's been proven that every time he's been left like that, he's gone and scored a lot of goals. He's world class.
"So that was the biggest mistake - I'm not going to blame anybody."
Asked if he blamed Mourinho for Bale's inconsistent form, Barnett replied: "Well, I wouldn't do that.
"He's a very successful coach… but Julius Caesar was also very good, but I don't think he would be very good with the armies now."