Cooke, who rejoined Hunslet from Keighley Cougars last October, was stretchered off in the first minute.
“He got his leg trapped awkwardly in a tackle,” Hunslet coach Gary Thornton said.
“He has been to hospital and there’s nothing broken, but there’s suspected fairly serious ligament or cartilage damage.
“We won’t know until the swelling goes down, he’ll probably need a scan to learn the full extent of it, but it looks fairly long-term as regards availability.”
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Duane Straugheir (rib) and Brad Hay (groin) also picked up minor knocks in the Parksiders’ 12-6 defeat.
It was Hunslet’s second and final practice match before they begin their Betfred League One campaign at home to Workington Town on Sunday, May 9.
Thornton’s men led 6-0, but conceded two late tries after they had Alex Rowe “very harshly” sin-binned and Thornton made a host of substitutions.
“We were very good,” the coach said. “They are everybody’s favourites [to win the title] so it was a fair measure of where we’re at.
“We got plenty out of it and I am relatively pleased with the way pre-season has gone.”
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