Tim Nanai-Williams may not be seen in a Chiefs jersey until late June, after being hospitalised with what's believed to be a stomach ulcer.
Nanai-Williams missed the 22-21 Super Rugby victory over the Force, and is likely to miss their two games before the June international window.
It's yet another blow to the defending champions, with coach Dave Rennie saying they're also likely to be without Gareth Anscombe for a while with a fractured foot.
"It's probably a five or six week injury so it means he'll miss the next three weeks. We've got a bye in there as well and then that June window, all things going well, he'll be back in time to face the Hurricanes.''
The Reds have beaten the Sharks 32-17 in Brisbane.