De Groot stepped into the captaincy role when flanker Billy Harmon cut his hand, and the pair will lead the side at the weekend.
Coach Clarke Dermody said, "Ethan's done a great job in Billy's absence, and it's about using both of them.
"So, we're using the skill sets Ethan's shown in the last couple of weeks, and it will take a bit of pressure off Billy with his first week coming back.
"They're different personalities, but together they're a pretty strong unit."
They will be without first five-eighths Cameron Millar after his head knock against the Blues last weekend. Ajay Falegaga will start.
Dermody said Falegaga had shown he was an emerging first five-eighths, had been playing club rugby and was fit and excited to have a chance to play in the side's final home game of the year.
Dermody was pleased to hear a charter flight from Fiji would arrive with fans before the game.
"That's awesome. We've got one of the best stadiums in the world, and when it's loud, it's even better. It will add to the occasion.
"It's a Sunday afternoon, which is new for us, but it's going to be cool to be able to celebrate with our fans and also the Fijian fans."
Dermody said the game would be a good challenge for the Highlanders.
"They're a dangerous team. If the game goes their way in the way they want to play then, as we've seen, and we've felt in the last few years, they've taken this competition by storm."
Dermody confirmed that Tanielu Tele'a has a grade two MCL injury, which can take three to six weeks to recover from.
Jona Nareki is back from injury on the left wing.
"He's excited. He was potentially available last week, but we gave him another week to get ready to make sure he hits all his high speed metrics because we knew this game was going to be important and to have him and Connor [Garden-Bachop] coming back into the team is a plus for us."
The Highlanders are wary of the Drua scrum.
"Statistically, they're the best scrum in the competition. Greg Fleming's doing a great job with them. They've got a massive amount of raw power. There's a lot of technique going into their work."
He said the Highlanders pack is also improving and returning to the levels seen over the last few seasons.
