Redknapp, who expressed disappointment over the signal Bale has been getting from Mourinho, believes the Wales international needs somebody to believe in him at Spurs.
Bale has made just two Premier League starts for Tottenham under Mourinho since he re-joined the Premier League club from Real Madrid on loan last year.
The 31-year-old was left out of Tottenham’s squad that lost 5-4 against Everton in the FA Cup fifth-round tie on Wednesday.
“At the time I thought Gareth Bale would be an amazing signing,” Redknapp said on Friday’s talkSPORT Breakfast.
“I could see that forward line, Son, Bale and Kane, I thought ‘oh my God they are going to be scary together’, but for whatever reason, it hasn’t worked for Gareth.
“I know he has been one of the top players in the world, let’s be honest, there was a spell where for me he’d probably been the third best player around behind [Lionel] Messi and [Cristiano] Ronaldo, he was that good when he was at his best.
“But he’s still not a very confident boy. He’s one of those lads who, no matter how great you are, it doesn’t change his personality, and he’s a very quiet lad. He needs confidence, and he needs somebody to believe in him.
“At the moment he’s had ten minutes here, five minutes there, when he starts he gets subbed, and when he gets subbed it’s all, ‘we were better in that last half hour’ after Gareth has come off…
“All the signals he’s been getting [from Mourinho], I am disappointed with how it’s gone for him. I was really expecting big things from Gareth when he came back.”
Redknapp added, “I have said all along, I don’t think it [Bale joining Tottenham] was Jose’s move.
“I would think that was done above him, maybe Daniel [Levy, Tottenham chairman] looked and that, and he loves Gareth, obviously he was a great player when he was there.
“People at the club tell me they have got him back on a very low-paid deal, they are really not paying him anywhere near what he earns, I’d be surprised if they are paying more than a fifth or a sixth of what he actually earns there.
“They probably saw it as a great move, a great move for the club to have him back again and the fans will love it, but it just hasn’t worked out.
“At the end of the day the manager picks the team, and he obviously doesn’t seem to fancy him, he doesn’t fit in his team.”