All Black doctor Deb Robinson said this morning Hoeata had hurt his right shoulder in Taranaki's national provincial championship match against Bay of Plenty on Tuesday night.
"While he took part in All Blacks training yesterday afternoon, it was causing him enough concern to warrant further examination.
He will get a scan in Auckland later today and we will then be able to assess how serious it is."
A decision on whether Hoeata is fit to travel to South Africa will be made later today.
In the interim, Donnelly, who has played 15 tests, will train with the All Black squad at their final training run in Auckland today.
Donnelly is the second player, after Wellington's Victor Vito yesterday, to be called up as injury cover.
Coach Graham Henry was expected to name his squad for next weekend's Tri-Nations match against South Africa later today.
