But Saints also say their agreement with North has "not contravened any rules, laws or regulations".
Northampton are likely to be investigated by Premiership Rugby - and they could be hit with a five-figure fine - by allowing North to be available for international rugby this weekend.
The Australia game falls outside the International Rugby Board's official autumn window, and Premiership Rugby's policy is that no non-England players should subsequently be released for matches or training camps.
That policy was agreed by all 12 Aviva Premiership clubs, with any breaches governed by a code of conduct.
Bath prop Paul James has returned to the Recreation Ground this week, while Perpignan players James Hook and Luke Charteris have also left the Wales camp to rejoin their club.
North, 21, moved to Northampton from the Scarlets earlier this year.
He arrived at Franklin's Gardens after starring for the British and Irish Lions during their 2-1 Test series triumph against Australia in June and July.
In a statement, Northampton said: "The Saints management wants to make it clear that our agreement with George has not contravened any laws, rules or regulations.
"However, when it was finalised, the agreement included terms for his release to play international rugby which were outside Premiership Rugby board policy.
"George is a young man who is proud to represent his country. Indeed, the club's management wants every player at the club to achieve the highest level they can, and wants every player to have the ambition to wear their respective national shirt.
"The club is also committed to adding depth to the playing squad, and working with someone of George's calibre has benefited young, home-grown players like Jamie Elliott, Tom Collins and Howard Packman, all of whom have played first team rugby this season.
"The Saints management has sought to build a squad that can compete in every tournament.
"This involves both establishing a strong production line of local talent and bringing in world-class players when they become available.
"Sometimes this requires compromise, and while we appreciate that we are outside Premiership Rugby board policy with this particular agreement, we also believe that having George as a Northampton Saints player has benefited both the club and the league as a whole.
"George is a world-class player who in his short time at Franklin's Gardens has brought a great deal of excitement and quality, not just to the Saints but to the Aviva Premiership as a competition.
"When his signing was announced it was hailed in the media and by the league's hierarchy as a massive statement of intent by the club and a reflection of the competitive nature and high profile offered by the Aviva Premiership.
"Every player asks for specific conditions to be included in their agreements. This is not unusual in professional sport.
"In order to realise this rare opportunity of bringing a player like George to Franklin's Gardens we agreed to allow him to represent Wales if, and when, selected."