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 interested 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."
Bundee Aki and Tim Nanai-Williams comprise the Chiefs midfield for the Rebels match after their effective combination against the Sharks.
Many matches missed
• Two reconstructions on each shoulder.
• 17 tests in three years after making All Black debut v England in 2008.
• Last test was World Cup final v France in 2011.
• Has played four matches for Chiefs this season; 68 in total.
• Due at Japanese club Toshiba in August.
Read more: Is this it for Kahui's career?