Arsenal have signed Norway international Martin Odegaard from Real Madrid on a permanent deal.
The midfielder spent the latter half of last season on loan at Arsenal, making 20 appearances in all competitions and scoring twice, including in a 2-1 win over north London rivals Tottenham Hotspur.
Arsenal did not reveal financial details of the transfer announced on Friday but British media reported they had agreed to pay around 35 million euros ($A57.32 million) for him.
Odegaard joined Real aged 16 and became their youngest ever player but made only 11 appearances in all competitions, starting six games.
The 22-year-old will not be available for Sunday's game against Chelsea as the club are awaiting visa clearance, they said.
Australian Associated Press