The club are beginning a search for someone who can replace the Australian, however.
“Shannon has snapped his achilles. He gets surgery today, so we move on and try and find another full-back,” he said.
“You’ve got to feel for Shannon, you genuinely have to feel for him.
“Then he goes and has a major injury, which is disappointing for Shannon and disappointing for everybody concerned.
“As a club we’re used to adversity and we’re used to all these things. We’re used to picking up major injuries, we’ve had plenty of them this year.
“We’ll move and someone else will take that spot and we’ll be comfortable.”
Meanwhile, Cunningham conceded that his team were beaten by a better Castleford side in last Friday’s thriller at The Jungle.
“In the second half I thought Castleford were the better side,” he said.
“We seemed like we were just hanging in there for a lot of it. We stil scored some tries.
“All credit to my players, their determination to still hang in there even though they weren’t great was magical.
“But the deserved side won.”