Sunderland boss Keane will be without Edwards (left) and Richardson

The 22-year-old Richardson has been ruled out for up to three months with a stress fracture of the back.

And winger Carlos Edwards, 28, is likely to miss the next four games after suffering a setback in his bid to return from a hamstring injury.

Edwards was in line to face Reading on Saturday but broke down in training.

The news will come to a huge blow to manager Roy Keane, who has already lost skipper Dean Whitehead for six months with a cruciate knee injury.

Summer signing Richardson went off injured after 20 minutes of the home game against Liverpool last month and tests have revealed that the injury was worse than first feared.

It's a setback for the lad and for us because he's a big player for us Roy Keane on Carlos Edwards

Keane said: "We've had bad news on Kieran. He saw a specialist this week and he has a stress fracture of his back.

"We'll have more news after he sees a surgeon but 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."

Edwards has not played since Sunderland's 2-2 draw against Birmingham in the first week of the season.

He suffered a hamstring tear and has missed the last three Premier League matches but was close to making a first-team return.

"It's not the same injury but it's a similar type of injury in the same area," added Keane. "It's a setback for the lad and for us because he's a big player for us.

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"It's the downside with hamstring injuries. We look at injuries, we look at players' recovery but one thing we don't do is push them too much, it's just one of those things.

"He had a week's running with the medical staff and then he trained with us, he was doing OK and then he walked off saying he felt something. It's a blow."