The talismanic stand-off was taken there by ambulance after suffering a back injury when being tackled in yesterday’s 28-28 draw at Dewsbury Rams.
The Championship part-timers - who have reached the last four for the first time in more than 30 years - are given little chance of causing a shock against Super League leaders Saints.
However, it will be harsh on Murrell if he misses the occasion; as a youngster at Hull KR, he had to sit out the 2006 Challenge Cup semi-final due to injury - the last time a second-tier club had got so far - and, at the age of 33, he has still yet to experience one.
Grix said: “There was a bit of a worry, a real concern that he’d done something a bit more serious.
“But it was one of those; he’s done what a good half-back should do… gone into the line, turns to play out the back and you are exposed in a position where you can’t see what’s coming behind you.
“But it wasn’t a bad one (tackle) by any means. It was fractionally late if anything but it’s as he’s letting go of the ball and I’m sure we’ve done worse throughout this year.”
Murrell was meant to be at the semi-final media day at University of Bolton Stadium today but Jacob Fairbank took his place instead.
Grix added: “He was supposed to come with us but he spent time getting scanned and everything in hospital last night and then woke up this morning really stiff due to the whiplash.
“He didn’t want to come sit here upright all afternoon.
“Hopefully, all being well - he’s our captain, our leader on the pitch - we can get him out there and that would go a long way to doing the things we need to do; performing well and maintaining our standards.”
Meanwhile, Hull's own pivotal half-back - Marc Sneyd - was also absent from the media event after suffering back and shoulder injuries in yesterday's win at Leeds Rhinos.
But head coach Lee Radford expects him to be fine for Saturday's semi-final against Warrington Wolves and also added that Albert Kelly has bee passed fit to make his own return.