"Last season I said the team needed a player who could add that 'X Factor', " he told liverpoolfc.tv.
"We wanted someone who could do something unbelievable and hurt the opposition when they were not expecting it.
"All the top teams have a player like that.
"We've relied on Stevie Gerrard to do that for us for a long time - but now Fernando has added another dimension to the side. For me, he has to be the best striker in the world.
"I'm delighted we've got him. His goal against Arsenal in the quarter-final second leg came out of nothing. It was a sharp turn and smashing shot.
"He also has unbelievable pace as well. He is like Michael Owen when he was 17 or 18, with that explosion over the first few yards.
"He's also similar to Ian Rush in a lot of ways. Not just because of his pace and goalscoring but also because of the work he does for the team.
"That certainly doesn't go unnoticed by the lads and supporters."