Springbok captain Warren Whiteley is a major doubt for South Africa's June internationals against Wales and England after being sidelined by a knee injury.
The loose forward, after missing much of the past year with groin and knee problems, suffered a new injury on Monday at training. He was made unavailable for Super Rugby's Johannesburg-based Lions, on the advice of an orthopaedic surgeon.
The Lions left for a four-game Australasian tour without Whitely and no date was given for the player's potential return.
"Warren Whiteley has not been medically cleared by the Lions Rugby Company medical team and will not join the Lions on tour until he is medically cleared," his team said on Thursday in a brief statement.
The Lions begin their tour of Australia and New Zealand on Friday night against the NSW Waratahs at Allianz Stadium, followed by matches against the Queensland Reds, Hurricanes and Highlanders.
The potential absence of the No.8, along with lock Eben Etzebeth, will force the Springboks to select a replacement captain as they begin a new era under recently appointed coach Rassie Erasmus.
Mieanwhile, England centre Jonathan Joseph is set to miss the three test tour of South Africa in June after being ruled out for the rest of the season due to injury.
The 26-year-old hurt his left ankle during the first half of his club Bath's 41-6 defeat to Saracens on Sunday and needed crutches to leave the field before his foot was put into a protective boot.
"JJ is going to need surgery to correct his injury. He will then need a lengthy period of time to rehabilitate," Bath's Director of Rugby Todd Blackadder told the club's website.
England start the tour against the Springboks in Johannesburg on June 9 and Joseph, capped 40 times, had been due to play a prominent role.
South Africa play Wales in June in Washington before three home Tests against England.
