Brad Shields faces six weeks on the sidelines after suffering ligament damage in his foot, says England assistant coach John Mitchell.
Shields returned home early from England's warm-weather training camp in Italy last week and was replaced by Alex Dombrandt.
Asked about Shields' diagnosis, Mitchell said: "Brad's got a tear in the lower foot. It's always a little bit niggly, but it's four to six weeks for him."
Shields is on course to be fit for England's World Cup opener against Tonga on September 22 but could miss all four of their warm-up matches.
England take on Wales at Twickenham on August 11, Wales in Cardiff on August 17, Ireland at Twickenham on August 24 and Italy in Newcastle on September 6.
Shields' injury will be a concern to Eddie Jones, who will name his 31-man squad for the World Cup in Japan on August 12.
The head coach already has Mako Vunipola, George Kruis and Jack Nowell recovering from injuries, as well as the New Zealand-born Shields, who has eight caps for England.