John was a last-minute addition to the Scotland squad due to doubts over Ally Hogg's fitness. John had been due to play for Scotland's U21 side in their World Championships in France.
Hogg faced the South Africans but injuries to Jason White and Donnie Macfadyen means that John will be staying with the senior squad. John wasn't in the squad for last week's match and it had been expected that he would be released to join the U21s.
"If the game was being played tomorrow, Johnny is in the side," Hadden said. "There are four fit back row and he is one of them. Until that changes, he has to stay."