Richardson joined Sunderland this summer from Manchester United.
Sunderland boss Roy Keane said: “We’ll have more news after he sees a surgeon later today.
“I would have thought that he’ll be out for two to three months.
“It’s a major disappointment. Kieran was able to do elements of training but it affected him when he twisted or hit the ball hard.
“In the last week or two we were hoping that it might settle down but clearly it’s a lot more serious.”
