Spain boss Fernando Hierro has admitted that he has concerns over his side's defence in the group stages of the World Cup.

The Spaniards conceded the most goals out of the four teams in Group B, despite finishing top of the table after drawing to Morocco on Monday.

The team will play Russia in the Round of 16 on July 1, and Hierro is wary that his side must improve defensively if they want to prosper in the remainder of the tournament.

"Obviously we can improve, there are things that definitely need to be worked on, and we will definitely be self-critical," Hierro told reporters after the game.

"Five goals in three matches is not the way forward, I've told the players that. But they are professionals and understand.

"We have to be very demanding of ourselves, and be clear in our mind that if they score against us so easily it will be very difficult to reach the ultimate goal."

Hierro took over as Spain boss two days before their opening fixture against Portugal, after Spanish Football Federation president Luis Rubiales dismissed Julen Lopetegui for agreeing to become the new Real Madrid manager.