Richards is currently in his second spell with the Exiles

Richards, who picked up the injury in the win against Treviso on Saturday, has had an operation to repair a torn biceps muscle in his left arm.

The 29-year-old had surgery after a scan revealed damage to the tendon.

London Irish say the operation was "successful" and they expect Richards to be out of action for three months.

Richards left the pitch at half-time on Saturday, having scored Irish's opening try as the Exiles qualified for the quarter-finals of the Heineken Cup for the first time in their history.

He last appeared for England as a substitute in the World Cup final against South Africa in October. He was included in Brian Ashton's squad of 32 for the Six Nations.

His injury may open the way for team-mate Paul Hodgson to receive his first England call-up. The scrum-half is currently in the Saxons squad and was called in to join the main squad's training session at Twickenham.

England begin their Six Nations campaign on the 2 February 2008 against Wales at Twickenham.