It is hoped that Grix will be able to leave hospital soon but he will not be fit enough to play for some weeks.
The Wolves face Catalans Dragons at the Stobart Stadium Halton on Sunday for a place at Wembley against either Leeds or St Helens.
“He’s picked up a viral strain of pneumonia and been quite severely hit,” coach Tony Smith told BBC Radio Manchester.
“We’ve had him in hospital in intensive care for a little while now and he’s on the mend and coming out very soon.”
Grix missed last weekend’s game against St Helens and it is expected he will not make his return for at least a few weeks.
“He’ll certainly miss this weekend and from the advice I’ve been given it’ll take him a little while to get his reserves back up to the right levels of fitness.
“Our thoughts go out to Simon because it’s a time of the year when you don’t want to miss games, but he’ll be back in no time I’m sure.”