Health has allowed Rennie to retain faith in the players that have helped the Chiefs win all three of their opening matches, but so too has form. While losing Retallick would be a blow for any side, the Chiefs are more than content with their contingency plans.
Fitzgerald and Symons started together in the wins over the Blues and Brumbies, while the pair played 70 minutes alongside each other last week.
"They've played a lot of footy," Rennie said of the locking duo. "They're going really well and we're really happy with them. They've just got massive work ethics - do a lot of graft for us - and they were a big part of our physicality in the weekend."
Another big part of that performance was the efforts off the bench of Bardoul. In just his second Super Rugby appearance, the Bay of Plenty loosie excelled against a formidable Crusaders forward pack.
"It was a pretty impressive performance," Rennie said. "He had a hand it all the tries, he handled the ball four times when Sonny scored, he stole a couple we scored off, so it was a massive day at the office for Johan.
"We're really rapt for him because he's not the most naturally skilled but he's worked really hard on his handling.He's great and he deserved another crack."
The same could be said for Heem, who has made a strong start to his first Super Rugby season and was part of an all-Tasman back three last weekend, but Rennie opted for the experienced and enthused Gear.
"We took Hosea out of the mix last week - we just wanted to get him a little quicker and sharper and more powerful. Obviously playing against the Highlanders, his old team, that presents a little bit of motivation for him as well."
The Chiefs as a team certainly lack no motivation, with the Highlanders the only side standing between them and heading away to South Africa unbeaten.
"We haven't made too many changes this week and that highlights the respect we have for the Highlanders," Rennie said. "They're a good side and it's an important weekend for all of us. If we get it right, then we head off to Africa with some good points in the bag."
Chiefs team to play the Highlanders at Waikato Stadium tomorrow:
Tom Marshall, Hosea Gear, Charlie Ngatai, Sonny Bill Williams, James Lowe, Aaron Cruden, Augustine Pulu, Liam Messam/Maama Vaipulu, Sam Cane, Johan Bardoul, Michael Fitzgerald, Matt Symons, Ben Tameifuna, Hika Elliot, Pauliasi Manu. Reserves: Quentin MacDonald, Siate Tokolahi, Mitchell Graham, Michael Allardice, Maama Vaipulu/Michael Leitch, Brad Weber, Damian McKenzie, Andrew Horrell.