George North will be out until the end of April after having further tests on a head injury.
The Welshman has now suffered three concussion in recent months and will spend some time on the sidelines.
Wales wing George North will not play for Northampton in Saturday's European Champions Cup quarter-final at Clermont Auvergne after his latest head injury.
North has been knocked unconscious three times in recent months, including in last Friday's 52-30 win over Wasps.
Winger George North says he's feeling OK after being knocked out during Northampton Saints' win over Wasps.
The Welshman suffered a knee to the head by Nathan Hughes, who was sent off for dangerous play but protested his innocence.
North was stretchered off unconscious and in a neck brace, but tweeted to say he was fine.
The Lions captain Sam Warburton has praised Australia for a "thrilling" test match in Brisbane.
"That was entertaining, that's for sure," he said in a pitch side interview with Sky Sports. "The last 20 minutes were so hard and we really had to dig in. Credit to Australia."
George North who scored a try in the first half has praised the travelling fans for "their fantastic support".