No 8 Mose Tuiali'i is the latest, having strained his knee and he will be out for about five weeks.
Tuiali'i (32) came into the squad at the start of the month, called up as injury cover for the injured Nasi Manu.
Manu went down in the first game of the season with a foot injury, and is out for the year.
Tuiali'i, who has spent the past four years playing in Japan, had looked promising in the two games he has played, getting around the paddock, and would have been keen to take on his old side the Crusaders.
But a knee strain, which worsened at training this week has failed to respond to treatment and he is out for more than a month. He is unlikely to make the trip to South Africa.
Elliot Dixon may have been an option at No 8, as he has more game time at this level off the back of the scrum, but there are question marks over his defence and ability to play the whole 80 minutes.
Highlanders coach Jamie Joseph has made a total of six changes to his team to take on the Crusaders tonight in Christchurch, and has gone with five forwards on the reserves bench.
All Black halfback Aaron Smith has won back his starting spot after being benched last week.
He responded to his dumping with a better effort when he came on for the final 30 minutes against the Brumbies last week, and scored a try.
Outside him is Hayden Parker, who put together an encouraging starting debut for the side last week, and his goalkicking will be vital for his team tonight.
In other changes, Otago outside back Tony Ensor comes in on the right wing, as both Kade Poki (ribs) and Buxton Popoali'i (foot) are unavailable, because of injury.
Jason Emery gets a start at centre and Phil Burleigh drops out of the squad.
The props have changed, with All Black Tony Woodcock available again, after missing a couple of games because of a hamstring injury.
Chris King comes in at tighthead prop and Ma'afu Fia, who has impressed of late, goes to the bench.
Jamie Mackintosh, who also played well in the loss to the Brumbies last week, is also among the replacements.
With Jake Paringatai also in the reserves, and getting his first chance for more than a month, Joseph has opted for just the two back reserves.
Wet weather is forecast for Christchurch tonight and with the Crusaders fielding an all All Black tight five, it may be a very competitive match up front.
The Highlanders have seven losses from as many games this season and know they have a bye after tonight's match, so they should not be lacking for motivation and energy.
Just two players from Southland are in the starting team and four from Otago.