Sam joined Sunderland in January 2017 when he penned a deal until the summer of 2019.
The youngster will link up with Ellliott Dickman’s under-23 squad, and moves to Wearside with a great pedigree despite only being 20.
With six senior New Zealand caps, Brotherton swapped Stateside for Wearside having represented the Wisconsin Badgers of the University of Wisconsin in the Big Ten Conference.
The 20-year-old sophomore defender was named National Soccer Coaches Association Player of the Week in October, becoming the first University of Wisconsin men’s soccer player to earn the award.
Brotherton also has experience at youth international level, representing New Zealand at under-20 and under-23 level.