The after-effects of a head knock have forced the Auckland Blues' flanker Justin Collins to pull out of Saturday night's Super 14 rugby match against the Crusaders.

Collins, who has played 103 Super rugby games, was concussed in the Blues' match against the Queensland Reds late last month.

Despite coming through training on Thursday, he later suffered headaches and was pulled from the Blues' final game of the season on Friday.

"It's tough on Justin. He is such a key figure and leader in our team and he desperately wanted to help his team-mates take on the Crusaders tomorrow night at Eden Park," coach Pat Lam said.

"But with these ongoing symptoms it's just not worth risking him out on the field."

Peter Saili will move into the No.6 jersey and newcomer Andrew van der Heijden will slot onto the bench.

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