The England winger has impressed in place of the injured Aaron Lennon.
"Do his displays in the last couple of weeks confirm how I've handled him? I wish I can say yes but it hasn't all been easy. He's been a problem and if Aaron doesn't get injured he probably doesn't play," said Redknapp.
"I played Niko at first, because I didn't really feel at that time that he deserved to play in all honesty. I had Niko and Luka as well, and I played Luka on the right. I just felt they were both happier on the left, so I brought David back in.
"I suppose other managers probably wouldn't have had the patience that I've shown with him. Everyone's different and I don't bear grudges.
"When I came here there was a group that weren't with the first team. There were about eight players who were sort of isolated. I've never done that. I'm not into sending players off to train on their own or send them off with the youth team.
"Was I hard on David? Probably not that hard. If I'd been really hard on him then I probably would have isolated him. He knows he wasn't doing what he should have been doing. I spoke to him about the situation and he accepted that he wasn't right, his attitude wasn't right, but he was finding it hard to pull himself out of it at that time.
"I think it's like anything, when he wasn't playing his head probably went down. He saw no light at the end of the tunnel. When you come in every day and you're not playing it's difficult. He's not been used to that. He's been at Blackburn, where he was a big player, and he's found it difficult. He couldn't accept it really.
"It's easy for us all to say 'well, he gets paid to do this'. Fine, but I do understand how he was feeling. Now he's back playing and he's enjoying being in the team, but it's only four or five games. You hope he can keep his attitude right and that he keeps playing as he is."