Cornish Pirates back Wes Davies could be out for up to six months after rupturing his calf muscle.
The 33-year-old former Wales rugby league player was hurt in training earlier this week.
"After being told it was just serious cramp he's had a major injury and he'll be out for three to six months," boss Chris Stirling told BBC Radio Cornwall.
Davies has played in six league games this season and scored tries in each of the Pirates last two games.
Stirling continued: "He's determined and if there's any chance that Wes can be back he will take that chance.
"He'll work hard on his rehab and we'll need him back in the team, he's such a crucial member of the squad," he added.
Davies is expected to have surgery on the injury in the next few days.