Ospreys flanker Sam Underhill has been ruled out for around four months because of a shoulder injury.
The 20-year-old open-side sustained the injury in training and will have surgery later this week.
After Underhill broke into Ospreys’ first team last season, England coach Eddie Jones said the back-rower could feature in the autumn internationals.
But Underhill, who has pledged his allegiance to England, is now in danger of missing the November Tests.
“Sam suffered a high grade AC joint injury in training last week,” said Chris Towers, medical performance manager at the Ospreys.
“The agreed course of action for Sam is for him to undergo surgery to reconstruct the damaged ligaments. That will take place at the end of the week before he commences a programme of rehabilitation.
“The initial prognosis is that he can expect to be sidelined for a period of around four months.”
Underhill impressed in his 16 appearances for Ospreys last season, having made his debut in September.
The former England Under-18 player was at Gloucester before moving to Wales to study economics at Cardiff University.
Born in the United States, Underhill could qualify for Wales in the future under the three-year residency rule.