The 19-year old Spanish defender has already played twice this season following the injury to Martin Skrtel but realises he needs to keep improving this season.
"I had been in the academy at Sevilla and straight away when I joined Liverpool, the club decided that I would join the reserve team," he told LFC Magazine.
"That was an immediate step up in quality for me from what I was used to in Spain. It was good for me, it was a very big challenge at an important moment in my career.
"I improved a lot playing in the reserve team. But now I have to keep improving. I have come a long way, but I still have even further to go."