London - Northampton and Wales wing George North will miss Saturday's European Champions Cup quarter-final with Clermont Auvergne after sustaining another head injury during an English Premiership match last week.
North, who also sustained two blows to the head in Wales's Six Nations defeat to England in February, appeared to be knocked out as he scored a try in Northampton's 52-30 victory over Wasps.
"We won't play him at the weekend. Clearly he had a nasty knock," Northampton coach Jim Mallinder told Sky Sports television.
"We've got to look after him and we must make sure the medical experts are happy and satisfied he is fit to return to play and as soon as they say he is, then we'll be happy to pick him again."
However, former World Rugby medical adviser and ex-Ireland international Barry O'Driscoll told the BBC that North should not be allowed to play again this season after so many concussions.
"There should be no more rugby for George North this rugby year," he said.
"Somebody who has four concussions in five months -- two in one game -- and is going back to such a brutal game as rugby should be having a long rest from rugby under the care of a neurologist."
Wasps forward Nathan Hughes was banned for three weeks on Tuesday by an RFU Disciplinary Panel following last Friday's incident.
The 23-year-old was sent off for his challenge on the winger, who was struck by Hughes' knee and knocked out as he scored Saints' second try of the match.