"It is clear that he must improve," said the Reds boss.
"He has given a lot to us but he must improve and he knows this. But the main thing for me is his mentality is really good, it is really positive and I know he will try to improve.
"He needs to train on specific things, change two or three details and also work on his strengths.
"We are not really surprised at the way Fernando has settled in because we were talking before we decided to sign him and we were talking about his pace, his physical strength and mentally.
"We knew that he had a very good character - so we were aware of all that. He wants to be successful here. He is really happy with the city and the supporters and everything so I think that the key is that we knew the player before.
"We had a list of strikers and we were looking for one with the right mentality for England, it's not just about quality.
"Also, the fact that Fernando is just 23 means that in terms of business and performance we have signed the right player."
