Northampton Saints and Wales wing George North will not play again this month on the advice of a neurologist.
The 22-year-old, who was knocked out during Friday's 52-30 Premiership win over Wasps, will be re-assessed at the end of April.
It was North's fourth head injury in the last five months.
Wasps forward Nathan Hughes was sent off for the incident that led to North being knocked unconscious and will appeal against his three-week ban.
Hughes, 23, was found guilty by a Rugby Football Union disciplinary panel of "striking with the knee and/or shin".
However, despite the appeal, he will not be able to play in Wasps' Champions Cup quarter-final at Toulon on Sunday.
In a statement Northampton said North would continue to be monitored by the club's medical team.
North will not take part in on-field training but will work to maintain his fitness with Saints' performance department.
"We have listened to the advice we sought and George will be taking some time away from the field," said director of rugby Jim Mallinder.
"Throughout this process, it is important that George's welfare comes first and that he is treated patiently and calmly, only returning to action when all of the medical team are happy for him to do so."
North will miss Saturday's Champions Cup quarter-final at Clermont Auvergne and the semi-final should they progress, as well as Premiership matches against Exeter and Saracens.
The former Scarlets wing missed Wales' 12-6 win over South Africa in the autumn internationals after being concussed against New Zealand, and was then struck twice on the head while playing against England during the Six Nations.
Former World Rugby medical adviser Dr Barry O'Driscoll said on Monday that North should not play again this season.