Melbourne - Injured Lions skipper Sam Warburton has been ruled out of Saturday's deciding Test against the Wallabies in a major blow for the tourists, team officials said Monday.
Scans revealed a "significant tear" in his left hamstring suffered late in the Lions' 16-15 second Test defeat by Australia at the weekend. The Welsh flank will now miss the series showdown in Sydney, the officials said.
Irish veteran centre Brian O'Driscoll is now expected to captain the tourists in what will be his final Lions Test.
Warburton was helped off 13 minutes from the end of the second Test and remained in Melbourne after the match under the supervision of Lions team doctor Eanna Falvey to undergo a full medical assessment.
The loss of Warburton, their best player in the second Test, is a significant blow for the Lions as they strive to end a 16-year series drought.
"It is incredibly disappointing to be ruled out of the tour through injury as we head to Sydney for the deciding match," Warburton said in a team statement.
"I wish the team all the best and hope I can play some part in the build-up this week.
"I am confident that the boys can finish the job off and secure the series win."
The devastating news for the 24-year-old forward, who missed the Lions' opening two wins in Hong Kong and Perth with knee ligament damage, comes as he found outstanding form in the second Test.
Warburton became the youngest Welsh Lions tour captain in Lions history when he was named skipper in May.
He led Wales to the 2011 World Cup semi-finals, only to be sent off in a narrow defeat by France in Auckland.
Warburton was sent off after only 17 minutes for a spear tackle on Vincent Clerc and received a three-week ban.
After he missed the early part of the last European season through injury, Warburton starred against Scotland and in the record 30-3 thrashing of England that lifted Wales to the Six Nations title.
The injury follows the loss of experienced forward pack leader and Irish lock Paul O'Connell. He suffered a broken arm in the tourists' 23-21 first Test win over the Wallabies in Brisbane.
Ireland's Sean O'Brien, highly regarded by the Wallabies after his starring display in a 2011 World Cup pool game upset over Australia, is in line to replace Warburton at number seven for Saturday's third Test.
Wallabies senior back Adam Ashley-Cooper labelled O'Brien a "class act".
"(Warburton) would be a huge loss but they have a lot of depth there in the back-row," the 79-Test centre said on Monday.
"They're certainly not lacking in any good number sevens."
Lions head coach Warren Gatland is due to announce his starting line-up for Sydney on Wednesday.