The injury-plagued Kahui has played four matches for the Chiefs this season after his comeback from shoulder surgery last year which caused him to miss the half of the Super Rugby season and ruled him out of the All Blacks frame.
A hamstring strain saw him scratched from the match against the Sharks at Waikato Stadium on Saturday but worse came a day later when he "popped" his shoulder again.
He has had two reconstructions on both joints and the strain his body has endured prompted him to sign with Japanese club Toshiba at the age of 27 rather than stay and seek a return to the black jersey.
Kahui helped out at the Chiefs' final training run yesterday before the team flew out for Melbourne and their game against the Rebels tomorrow night. On Monday he is due to be examined by the surgeon who performed the last operation.
"He's incredibly disappointed and frustrated but you wouldn't know it seeing him around the boys," Rennie said. "That's just the type of character that he is.
"Of course we're hopeful," Rennie replied when asked if Kahui could play for the Chiefs again this season.
"I feel for the guy because he's just had wretched luck over the last couple of years. The few games that we got out of him he's been phenomenal, probably as well as he's ever played, so it's incredibly frustrating for him. We're hoping for positive news."
Kahui's first game back this season was against the Highlanders in Hamilton on March 22. A week later he put in a man-of-the-match performance against the Blues at Mt Maunganui, scoring a try and looking the best back on the field.
His prospective employers in Japan will also be interesting in Monday's visit to the specialist - they won't look favourably on what will be considered increasingly damaged goods.
Kahui couldn't be reached for comment yesterday, but said in March ahead of his comeback that his regular injuries were a tough burden to bear.
"Obviously you want to be part of it. You don't play rugby to sit on the sidelines but for the past few years it's happened more and more to me," he said.
Bundee Aki and Tim Nanai-Williams make up the Chiefs midfield for the Rebels match after their effective combination against the Sharks.
Changes have come at prop where Pauliasi Manu and Ben Tameifuna replace Toby Smith and the injured Michael Kainga respectively, at No8, where Matt Vant Leven will make his first start of the season, and at halfback, with Brendon Leonard in for Augustine Pulu.
Waikato player Vant Leven has the challenge of marking in-form Wallabies No8 Scott Higginbotham, who made life difficult for the Crusaders in his team's narrow loss in Christchurch at the weekend.
"Matt's our fifth No8 [of the season]," said Rennie. "Ross Filipo, Nick Crosswell, Fritz Lee and Michael Leitch, who is part of our wider training group, were all options but they are all injured. We're really happy with the way Matt went in pre-season. He's pretty uncomplicated, he's combative, so we're really excited for him."
Halfback Tawera Kerr-Barlow, who has been sidelined with a broken jaw, has travelled with the squad and will sit on the reserves bench if Patrick Osborne suffers a recurrence of his hamstring strain.
The Chiefs team to play the Rebels at Aami Park on Friday, kick-off 9.40pm NZT, is: Gareth Anscombe, Lelia Masaga, Tim Nanai-Williams, Bundee Aki, Aseali Tikoirotuma, Aaron Cruden, Brendon Leonard, Matt Vant Leven, Sam Cane, Liam Messam, Brodie Retallick, Craig Clarke (c), Ben Tameifuna, Mahonri Schwalger, Pauliasi Manu. Reserves: Hika Elliot, Toby Smith, Michael Fitzgerald, Tanerau Latimer, Augustine Pulu, Robbie Robinson, Patrick Osborne.
