The Chiefs remain unbeaten in the Super Rugby competition but their latest win's come at a cost with several players picking up injuries.
The 36-20 victory over the Stormers in Hamilton lifted the New Zealand conference leaders to three wins from three games and to second on the overall ladder.
The Chiefs are now sweating on the fitness of several players before they head to Perth and South Africa, with midfielder Charlie Ngatai and wing James Lowe set to miss the trip.
Rennie says Lowe is out for up to eight weeks with a knee strain while Ngatai will be sidelined for even longer with a calf injury.
And it's being reported that Ngatai's fellow midfielder Robbie Fruean has had a recurrence of his heart problems and may also be in doubt.