Ben Smith and Ryan Crotty under injury cloud for All Blacks

All Blacks fullback Ben Smith was found wanting under the high ball early. Photo / Greg Bowker

The All Blacks suffered a double injury blow in the opening half of the Lions series, with Ben Smith and Ryan Crotty both forced from the field.

Smith was substituted in the 26th minute after sustaining a blow to the head, while Crotty joined him on the sidelines after appearing to strain his hamstring in the 33rd minute.

Both players have suffered similar problems in the past and the pair's involvement in the rest of the series must now be in doubt.

Smith was sidelined for two weeks earlier in the Super Rugby season after sustaining a concussion while playing for the Highlanders. It was the fullback's fourth concussion in the past five years.

While little is yet known on the severity of Smith's current problem, the fact he was unable to return will leave the All Blacks taking a cautious approach with regard to their vice captain's health.

Smith was replaced tonight by Aaron Cruden as Beauden Barrett shifted to fullback, but the All Blacks do boast other options in their 33-man squad. Israel Dagg could take the No 15 jersey in the event Smith is unavailable, or the 20-year-old Jordie Barrett could be handed a starting debut.

Crotty, meanwhile, pulled up lame towards the end of the first half, immediately clutching at the back of his leg. The centre strained his hamstring in the All Blacks' loss to Ireland in Chicago last year, though that injury kept him out for only a couple of weeks.

The Crusaders man was replaced tonight by Anton Lienert-Brown and the Chiefs midfielder would almost certainly start alongside Sonny Bill Williams if Crotty's involvement is restricted in the rest of this series.

The uncapped Ngani Laumape is the other option in the All Blacks' 33-man squad, while young duo Rieko Ioane and Jordie Barrett are also capable of playing centre.

Blindside flanker Jerome Kaino also came off early in the second spell, being replaced by Ardie Savea, and was later seen heading down the tunnel. But it was unclear immediately whether the veteran had succumbed to injury.