Crusaders lock Sam Whitelock, pictured talking to team doctor Martin Swan in Wellington last weekend, will captain the side against the Highlanders in Dunedin.

Ryan Crotty is out, and Sam Whitelock is in.

When Crusaders coach Scott Robertson confirmed second five-eighth Crotty, the rock of his backline, couldn't play the Highlanders because of concussion issues he didn't attempt to downplay the significance of his departure.

"He is huge for us," Robertson said. "He is an on-field coach, passionate and plays well in every big game that we have had. So we will miss him."

GETTY IMAGES Ryan Crotty left the field early in a 29-19 loss to the Hurricanes.

If ever there was a game tailor-made for battle-hungry All Blacks midfielder Crotty, who had to leave the field early in the 29-19 loss to the Hurricanes last weekend after appearing to collide with a team-mate, it would be a Super Rugby match against the southern rivals inside the enclosed stadium in Dunedin on Saturday night.

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These are the sort of occasions where you need an old head to remain stony-faced when opponents are repeatedly firing shots and that is what Crotty has done over the years; he has been the glue that has helped keep the backline together. Now, in comes Tim Bateman, himself no novice at this level - his resume notes 78 appearances have been made for the Crusaders and Hurricanes since 2007 - at No 12.

"We made an early call with Ryan," Robertson stated. "With the amount of concussions he has had previously, it was the best thing to do. And to give him as much time to be ready, and the rest of the team know that. It was a bit of advice from the doc, and him personally, and just how he was feeling. He knows when he is right. He was okay, but not good enough to go through the HIA process early in the week."

The news in regards to captain and lock Whitelock is much better.

Whitelock, who was forced to retire soon after Crotty, will start at Forsyth Barr stadium and is set to resume his role of calling the lineouts and guiding the defending champions around the park.

Robertson said his skipper was so eager to get into his work that he had to be reminded to take it easy.

"He was fine after the game, was fine the next day and has been great all week," Robertson said. "With Sam it was really clear. The decision made itself around the HIA. As you go through the week, there are some clear processes you have to go through and he was fine."

Robertson admitted the early departures of Whitelock and Crotty at the Cake Tin caught him on the hop. Although openside flanker Matt Todd, another Super Rugby centurion, had captained the side in the past, the team was suddenly robbed of a massive amount of intellectual property and leadership.

"It actually got me," Robertson admitted. "That got me, the old two head knocks in pretty much the same play. We knew Toddy was going to be captain at that time, and obviously Luke Romano took over from Sam in the lineout calling.

"But the big thing is, you always keep big players on at the end of the game, to inject energy - and we didn't quite have it."

The job of tapping into the personnel on the reserves bench is going to be crucial. Against the Hurricanes, the Crusaders lacked fresh men due to the early departures because of injuries. As the defence coach Robertson is charged with ensuring his men counter the Highlanders' desire to play with speed.

"Tempo is critical and they have been very successful over the years in running teams off their feet. We are aware of that, we have defended it all pre-season."

Crusaders: David Havili, Seta Tamanivalu, Jack Goodhue, Tim Bateman, George Bridge, Mitchell Hunt, Mitchell Drummond, Jordan Taufua, Matt Todd, Heiden Bedwell-Curtis, Sam Whitelock, Scott Barrett, Michael Alaalatoa, Codie Taylor, Wyatt Crockett. Reserves: Ben Funnell, Chris King, Oliver Jager, Luke Romano, Billy Harmon, Bryn Hall, Mike Delany, Manasa Mataele.