England scrum-half Alex Mitchell is facing a prolonged spell on the sidelines after an operation to fix recurring hamstring issues.
The 29-year-old, who was Steve Borthwick's first-choice nine last season, has suffered four hamstring injuries this year.
The latest came in Northampton's win over Gloucester last month, ruling him out of England's Nations Championship campaign.
Mitchell suffered an injury to the same hamstring against Ireland in February and again against Fiji in July. He also tweaked his other hamstring - his left, non-kicking leg - in an England training camp in May.
Mitchell told the i Paper last month that he had been given the option, like skipper Maro Itoje, to skip England's summer fixtures against South Africa, Fiji and Argentina, but opted to play instead.
The prognosis for Mitchell's latest recovery is not yet clear, but the Six Nations begins in less than three months' time.
While Jack van Poortvliet has emerged as Borthwick's starting pick in Mitchell's absence, there is competition behind the Leicester man with Bristol's Harry Randall, Bath's Ben Spencer and Mitchell's club team-mate Archie McParland all vying for position.
Mitchell travelled to Finland to be operated on by Lasse Lempainen, a specialist in elite sporting injuries.
Chelsea and England defender Reece James and Paris St-Germain's Ballon D'Or winner Ousmane Dembele are among Lempainen's previous patients, both returning to consistent playing time after a string of muscular injuries.
Mitchell's England team-mate Ben Curry was also operated on by Lempainen and has made a successful return to action after 10 months out, featuring in England's win over Australia last weekend.
Curry posted "hamstring final boss" beneath an Instagram post marking Mitchell's operation.