The Aston Villa striker and Manchester City defender depart from the squad ahead of their qualifier with Gary Speed's side due to groin and hamstring injuries respectively
The FA confirmed that defender Richards, who is believed to have picked up a hamstring injury, withdrew after training on Saturday and has returned to Manchester City for treatment.
Bent had not been able to train ahead of Friday's win over Bulgaria after a groin problem and has gone back to Aston Villa.
England recorded a 3-0 win away to Bulgaria thanks to a brace from Wayne Rooney and a first Three Lions goal for centre-back Gary Cahill.
No replacements have been called up to the England squad ahead of Tuesday's Euro 2012 qualifying match at Wembley against Wales, who go into the match on a high after defeating Montenegro 2-1.