The former Hammers goalkeeper reckons indulging Cole's creativity held the player back because he struggled when his team were not in possession.
Hislop, 42, said: 'Harry kind of liked Joe just to express himself, and we'd play around him, or around Joe's unpredictability.
Days gone by: Harry Redknapp encouraged Joe Cole to express himself
'Encouraging him to be himself didn't help him. When you sign him you identify that, talented though he is, when we don't have the ball he's got to give us something else.
'Everything about his game on that side, when your team don't have possession, he simply wasn't good enough. Harry did not help him in that respect.
'But that is exactly like Harry. He wants players to come and just play naturally and he would fill the gaps around that.
'He allowed (Gareth) Bale to express himself last season and it was the same when we were at West Ham with (Paolo) Di Canio. He would be allowed to do exactly what he wants and we would fill the gaps around him.
Reborn: Cole has thrived since joining Lille on loan from Liverpool this summer
'And it worked - you can't take that away from Harry. But in Joe's case, in terms of stepping up that extra level, it held him back a bit.'
Cole, who has joined Lille on a season-long loan from Liverpool, scored his first goal for five months in a 1-1 draw with Lorient last weekend and will face Trabzonspor in the Champions League on Tuesday night.
Hislop, now a pundit on ESPNsoccernet's Press Pass, believes the French club is the ideal place for Cole, 29, to learn how to contribute when his team do not have the ball.
He said: 'He's in the mode of player of (Glenn) Hoddle and (Chris) Waddle, who both went out to France and did well. Cole's the same type of player.
Benched: Cole struggled to make an impact at Anfield and was loaned out
'I know Joe well, I like him a lot. We were at West Ham together and I hope he rediscovers his form.
'(But) you have to bring more than just that type of natural, unbridled ability. You have to be tactically aware and contribute so much more than when you're on the ball. This is an opportunity for Joe to learn that, but still does what comes naturally to him.
'In England, results are so important. It's a steep learning curve and you're not given much time, either. So maybe he'll get that at Lille.
'I don't think he got that at West Ham. Certainly not under Harry. I don't think he was coached in that way.'
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