The 33 year-old has had an operation on a groin problem, but the Villans medical staff are still baffled by his ailment, and Lambert now admits that his chances of representing his country soon are slim.
"He's had an operation, but it's still underlying, it's not clearing up," Lambert told reporters.
"He's still struggling with the injury, which is a bit of a pain, we need to get to the bottom of that."
Ireland manager Giovanni Trapattoni is desperate for his defensive star to find fitness before the most important game in Ireland's group as they look to qualify for Rio in 2014.
Dunne is thought to have targeted a return to the starting line-up against Tottenham on October 7, but Lambert now thinks that the game may come too soon for the former Manchester City man.
When the defender does make his way back to fitness in time he faces a battle to regain his place in the first team as his fellow countryman Cieran Clark, who has been overlooked in the past by Trapattoni, and Dutchman Ron Vlaar are beginning to form a defensive partnership in Villa's back line.