That left Henare with little choice but to plump for youth, injecting the squad with a rejuvenated yet untested look.
While Rusbatch and Delany are all starring at the NBL level, Karena is the bolter in the bunch.
The centre recently finished his college career at Wright State, and has put in mixed showings with the Canterbury Rams since returning to New Zealand.
Karena is currently averaging 7.6 points and 3.4 rebounds per game on 48% shooting, and has been prone to defensive lapses.
However, he is potent offensively and Henare says he provides much-needed size with the absence of four legitimate centre options from the squad.
"He's a big strong lad and he's a big strong body and that's something that we are always looking for."
Henare says form is now vital to being picked in the squad, with the upcoming time crunch of the international schedule not lending itself to trials.
"I wanted to make it clear to everyone playing in the New Zealand league, to all our guys in the college system and playing overseas, that your form in whatever competition you are playing are essentially your Tall Blacks trials."
While the array of absences creates deserving opportunities for rising talent, it also significantly reduces the Tall Blacks' chances of qualifying for the Olympics.
A tough path requires the Tall Blacks to eclipse the likes of France, Turkey and Canada to claim the one available spot in Rio; nations which would all be objectively be favoured to win a potential matchup.
However, the return of much improved point guard Tai Webster creates a potentially potent lineup alongside brother Corey, Tom Abercrombie, Mika Vukona and Isaac Fotu; all players who all have experience of troubling their highly-fancied opponents.
A comprehensive build-up will help matters too, with visits to Japan and China before the squad is cut to 12. Those 12 will then travel to Latvia and Lithuania before the squad lands in Manila for their crucial qualifying clash against the Philippines on the 6th of July.
Tall Blacks: Tai Webster, Shea Ili, Jarrod Kenny, Corey Webster, Everard Bartlett, Ethan Rusbatch, Tom Abercrombie, Jordan Ngatai, BJ Anthony, Finn Delany, Mika Vukona, Isaac Fotu, Rob Loe, Michael Karena.