The 19 year old defender has been watching Johnson since his arrival from Portsmouth in the Summer and is looking to learn from the England right-back.
"He's a great player - England's first-choice right-back. There's no one better to model yourself on. It's great to watch him and play with him in training," said Kelly.
"I thought I did well against Lyon. It was my debut and there was pressure - it was my big chance. I thought I took it well.
"Rafa picks the team and there is a great squad here, but as long as I am in and around the squad and training with them, then it can only help me. If I keep working hard I hope I'll get another chance."