The Swans are expected to lose the on-loan Hoffenheim midfielder.
"If Sigurdsson leaves, we will need an attacking midfielder but, more than that position, we need goals," he told the South Wales Evening Post.
"We have to look at the players we have got and know more or less how many goals they will guarantee.
"You have to reach a certain number of goals otherwise you have to defend very, very well.
"If you lose a player who scores seven, eight or nine goals, you have to find another one.
"It is also good if you can find a player who can cover two or maybe three positions, because that makes it easier to change things."