The England man capped a breathtaking start to his Pompey career with a debut goal against Chelsea last weekend. His instant impact came less than 48 hours after arriving at Fratton Park on a frenetic transfer-deadline day.
And he told the Portsmouth News: "Against Chelsea I worked hard but sometimes it's difficult when you haven't played. It takes time to get your sharpness and fitness.
"To be honest, physically I felt really strong and I think if you prepare right then you feel good. But I definitely wasn't at 100 per cent. I will take the goal but there's still plenty more to come from me, it will just take a little time.
"I'm just going to keep training, keep working hard. The more games you play, the more you are sharper, fitter and the stronger. It's great to be here, especially with someone like Harry Redknapp as manager.
"He's a top manager. I was with him when I was really young at West Ham. He gives you that belief and confidence, something that I needed.
"It's been great and I'm now looking to build on that Chelsea start."