The Wallabies face South Africa, Argentina and New Zealand in July and August as part of the Rugby Championship, ahead of the World Cup in September.
Douglas, who has 14 caps for Australia, joined Leinster last summer after the 26-year-old ended his Waratahs career with the 2014 Super Rugby title.
His first season in Ireland saw Leinster finish fifth in the GUINNESS PRO12 and suffer an extra-time defeat at the hands of Toulon in their European Champions Cup semi-final.
Easterby said: "We are delighted for Kane and wish him well as he seeks the form and fitness required for selection for the Rugby Championship and, of course, the Rugby World Cup after that.
"Zane Kirchner is also in the initial South African squad and likewise we wish him well. It reflects very positively on Leinster Rugby when we have players selected for national squads.
"Our players should aspire to play at as high a level as possible, whether that be with Ireland or with their home nation."
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