Leicester Tigers captain Ed Slater will be sidelined for up to nine months because of a knee injury.
Second row Slater was part of England's Elite Player Squad last season and was injured playing for the England midweek side on the summer tour of New Zealand.
Director of rugby Richard Cockerill told BBC 5 Live: "The likelihood is seven to nine months and that's probably his season over.
"It's pretty horrific for Ed and pretty average for us."
Slater, who signed a new two-year contract with Tigers in November last year, has had surgery and started his rehabilitation.
Cockerill felt the 26-year-old would have been a strong contender to win full international honours this season.
"Certainly competing with Joe Launchbury, it would be a good contest between the two of them," Cockerill said.
"He's had some really, really bad luck. We'll look after him, get him right, and no doubt he will push for England honours again.
"He'll come back fitter and fresher than ever, hopefully that will be by this time next year."