South Africa international Schalk Burger has contracted bacterial meningitis after undergoing an operation.
Burger's family confirmed in a statement that the 29-year-old Springboks and Stormers flanker had surgery to reduce pressure on a nerve that was affecting his calf muscle.
"We as a family herewith would like to advise all the fans, supporters, sponsors and employers of Schalk that he was yesterday afternoon diagnosed as having contracted bacterial meningitis following an operation to reduce pressure on a nerve that was influencing the performance of his calf muscle," read the statement, which was published on the Stormers' website.
"Given a successful recovery, he will remain in hospital for the next 14 days. It will be at least another six weeks before he will be fit for playing.
"We would like to thank the specialists looking after him, and are doing a marvellous job, as well as everyone who has sent their best wishes, given the tough time he, his wife Michele and son Schalk are going through.
"We will issue a further statement as his condition improves."
Burger, a member of South Africa's 2007 World Cup final-winning team against England in Paris and a former world player of the year, has won 68 caps.
But he has not played since suffering a knee injury early last year, before calf-muscle trouble delayed his anticipated return in this season's Super Rugby competition.