Boxall was one of five players released by Wellington Phoenix after its elimination from the A-League finals by Melbourne City on Sunday.
It heightened speculation that the 26 year-old New Zealand international had agreed to terms with SuperSport United, which also has ex-Phoenix striker Jeremy Brockie on its books.
News website sowetanlive.co.za reported Boxall will join the Pretoria-based club for pre-season training in late June after signing a one-year deal on a free transfer.
He will reportedly fill a defensive hole identified by coach Gordon Igesund.
Boxall replaced the injured Winston Reid as captain for the All Whites' 1-0 Korea Republic in March, his 12th cap.
In his just-completed third season with Phoenix he started in eight of his 18 appearances, mostly at right back.
A former Auckland City FC defender, Boxall has had stints in North America, including a full season with Vancouver Whitecaps.
Brockie signed for SuperSport in January and has scored seven goals for his new club.