England captain Dylan Hartley has been ruled out of the summer tour of South Africa because of concussion.
The Northampton hooker has not played since sustaining a head injury in last month's Six Nations loss to Ireland.
Following specialist medical advice, the 32-year-old will now take an extended period of rest.
"It has been recommended that I take a break this summer and while I find that decision hard to accept, it's important I listen to that advice," he said.
England face the Springboks in three Tests, starting in Johannesburg on 9 June.
Hartley suffered a series of concussions two years ago, but returned to lead his country on the tour of Australia in June 2016.
He said he was "very disappointed" to miss the remainder of this season and is looking to return to action in time for the next campaign.
"I intend to use this time to recover fully from my injury, so I can be ready to hit the ground running when pre-season training starts later this summer," he added.
Forwards Courtney Lawes (Northampton Saints) and Nathan Hughes (Wasps) were ruled out in March with knee ligament injuries.
Meanwhile, former England flanker Steffon Armitage has ruptured an Achilles tendon and will be out of action for up to nine months, his French club Pau said.