Addo-Carr was forced off the field in the 77th minute with an abdominal injury, opening the door for Clint Gutherson to come on.
The Canterbury star was spotted on the sidelines with his hamstring heavily laced with ice.
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He was seen walking nervously in the dressing room but NSW coach Fitttler downplayed the seriousness of the injury.
“I think he’s good, I think he’s good,” Fittler said
“I think he was looking for relief.”
However, Canterbury general manager Phil Gould appeared concerned about Addo-Carr’s progress.
“Fox was straight and limp. It didn’t look good at all,” Gould said.
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If it’s too serious, he could return for the club’s 21st game against Penrith next Sunday or the 22nd game against the Dolphins the following week.
Canterbury are on the brink of finals contention and need to go on to win six of their last eight games to be any chance of winning eight.
Addo-Carr was one of NSW’s best performers in three games, scoring a try that has been compared to Billy Slater’s chip and chasing down an Origin classic with a speed of 134 meters.
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