Giant prop Ben Afeaki lasted all of four minutes before being sidelined by a broken arm that will take three months to heal. Fellow front-rower Toby Smith has pulled a calf and will be gone for up to six weeks.
"It's a massive concern and it's going to test our depth," Rennie said.
The fear all along has been there was not much point in having an Armani backline matched with a Cotton On pack.
The Chiefs did nothing to alleviate that angst.
"We were pretty keen to get a couple of our big fellas in midfield to carry a bit of ball and apply a bit of pressure, but we lost Ben in the first few minutes and came under a little bit of pressure in the scrum," Rennie said.
"We played a fair bit of footy at the wrong end of the field, and that pressure told."
Somehow, the Chiefs were handed the opportunity to win the game late, but three attempts at a lineout drive were poorly executed.
"We got outmuscled in the collision area and everything escalated from there," was Rennie's assessment of his side's shortcomings.
With Afeaki and Smith facing a combined 16-18 weeks on the sidelines, hope is fading for a dramatic turnaround in front-five fortunes.
Shane Cleaver, Ben Tameifuna and Alisona Taumalolo remain standing of the Chiefs' front-row resources.
Forwards coach Tom Coventry will earn his shekels in the next month trying to wheedle some quality out of what could be a struggling tight five.
Slightly more than 12,000 people turned up to watch the Chiefs, a decent enough figure, but still slightly disappointing given the fine weather and the start of a new era.
But can you blame Hamiltonians for staying away when the Chiefs have such a macabre home record?
Since the 2010 season, when the franchise started its tailspin, the Chiefs have lost 10 matches at home, while winning four and drawing two.
Hamiltonians are not going to turn up on faith any more. Chief executive Gary Dawson will be nervously listening for the click of the turnstiles on Friday.
If you can't get the public along for a derby against the Blues, then you really know you're in trouble.