The club confirmed on Friday afternoon that what was previously thought to be a "minor bump" has turned out to be an injury to his meniscus in the left knee.
It required an arthroscopic procedure which has ruled him out for the remainder of the season, and would ordinarily require a return to play of between 8 and 12 weeks.
Already missing fellow hooker Aaron Booth, the club's depth in the number nine jersey will now be stretched to the maximum.
Of their 22-man squad for this week's game against the St George Illawarra Dragons at Kogarah on Sunday afternoon, there are no other specialist dummy halves.
As it was, Clark was only moved back to hooker to cover for the injury to Booth.
Clark started the season at hooker, however, ultimately wound up playing at lock after a struggle to find form or consistency in the spine position.
Boyd playing 80 minutes at dummy half seems unlikely, so it will be intriguing to see what contingency plan coach Justin Holbrook lands on for the clash against the Red V.