Lions assistant coach Rob Howley said: "James had a blow to his head and his neck and he will have on-going medical assessment over the next 24 hours. Today is quite an important day for James with regards to the rest of his tour.
"He was the victim of a highish tackle and is feeling a bit groggy. James came out as a replacement and he has done particularly well.
"His match winning kick against Western Province, and his accuracy, have been invaluable. James has the ability to play at 10, 12 and 15 and losing a player of his quality is a blow.
The 12 hour citing window closed this morning and none of the Southern Kings players will be subject to any disciplinary action.
"There was a cynical mark on the game," admitted Howley. "There were a number of off the ball incidents that weren't picked up by the referee or touch judges.
"In the end, we were happy to come away with the win, draw a line under it and move on.
"The Southern Kings were very physical and there were incidents in the game, particularly with Gordon D'Arcy off the ball, which happened twice, which for whatever reason went undetected."