Giovanni Trapattoni has revealed that the 24-year-old is still suffering from the disappointment of their Euro 2012 campaign, when they were knocked out without winning a point.
The Italian said that he has discussed the situation with Gibson, who remains a "key player" for Ireland as they strive for qualification to the 2014 World Cup in Brazil.
"When Darron informed me of his decision to withdraw, I called him to talk things through," said the 73-year-old. "As we embark upon a brand new campaign, he is very much in my plans and I consider him to be a key player for Ireland for this campaign.
"However, Darron has said that although he doesn't want to let anyone down, he doesn't feel ready to to return to the squad for this fixture after the disappointment of Euro 2012.
"I hope that Darron will take this time to reflect positively on his international career, and return to us in time for the Germany game in October."
Sunderland's David Meyler has been called up as his replacement for the game on September 7.