Former All Blacks number eight Zinzan Brooke admits he's worried about New Zealand meeting England in the Rugby World Cup knockout phase, the two sides on course for a semi-final showdown.

Ryan Crotty. Source: Photosport

With both sides through to this weekend's quarter-finals, with the All Blacks facing Ireland and England against Australia, two victories would confirm Brooke's fears.

Speaking to the Rugby Paper, Brooke says he sees a possible All Blacks-England match-up as too close to call.

"I do fear the England semifinal," Brooke said.

"If the two teams do meet, which I expect them to, it could come down to a toss of the coin on the day. Top sport is about close margins and I can't see much between them.

"I'd like to say 'yes, New Zealand are going to win' but I don't confidently see it that way."