England full-back Mike Brown has been cleared of concussion symptoms and has returned to non-contact training, three months before the World Cup begins.
The 29-year-old has not played since March's Six Nations win over France.
Harlequins' Brown was initially knocked out in the Six Nations victory over Italy in February and was left out of the next match against Ireland.
He has now joined up with a small group of players in Bagshot, Surrey, before the full training camp on 22 June.
The group consists of players who were not involved in the Premiership play-offs, and includes Ben Morgan, Jack Nowell, Danny Care and Joe Marler.
After playing against France Brown had complained of suffering from headaches and did not feature for his club Harlequins for the remainder of the season.
Harlequins prop Marler, 24, missed the end of the season with a shoulder injury, while Gloucester number eight Morgan, 26, was ruled out of the Six Nations with a fractured leg.
The full England squad will travel to Denver, Colorado, later this month to begin preparations for the home World Cup, which begins on 18 September with England against Fiji.