Ash Dixon, who was appointed co-captain of the Highlanders last month, injured his back at training late last month and has been away from the training paddock since.
Highlanders coach Tony Brown said Dixon had received some positive news about his back but it was unclear when he would return to the field.
He could be back some time this season but an exact date was still not known.
Dixon had lost feeling in his back for a few minutes after the injury and was taken to hospital, although he was not kept in overnight. Rest seems to be the best healing option at present.
Auckland hooker Greg Pleasants-Tate damaged his knee in the side’s opening warm-up game against the Crusaders last Saturday.
Brown said the hooker would not require an operation and would look to rehabilitate the injury through rest and exercise but, like Dixon, when he would get back on the paddock was still unclear.
Pleasants-Tate is in his second season with the Highlanders, while Dixon is in his third year with the franchise.
He has made rapid advances over the past couple of seasons and was captain of New Zealand Maori side on an end-of-year tour.
The Maori will play the British and Irish Lions in June, so that will be a game Dixon will be targeting.
With Dixon and Pleasants-Tate out for the foreseeable future, Liam Coltman is the only hooker from the original squad still available.
North Harbour’s Adrian Smith has been training with the squad as cover for Coltman in the pre-season and will remain with the franchise.He is part of the side’s tens squad and Coltman is also playing at the tournament.
Brown said they were looking around for another hooker and searching through the ranks. Otago hooker Sam Anderson-Heather had made himself unavailable.
With each squad wanting three hookers and only 14 provincial teams in the Mitre 10 Cup there are not many rakes around.
Waikato hooker Hame Faiva joined the Highlanders last year as a short-term injury replacement but has joined the Blues this season.
Brown will head to Australia on Sunday along with the side’s All Blacks and players who have returned from playing in Japan.
The side will then all come together on Monday in Sydney to begin preparation for the final pre-season game against the Waratahs next Thursday.
The match is scheduled to be played at Concord Oval in Sydney.
The Highlanders’ first competition game is only two weeks away, when it takes on the Chiefs at Forsyth Barr Stadium on February 24.
Brown said the start may catch a few people by surprise as it had come around quickly and the All Blacks had only just got back into training.