The director confessed that he found it difficult to choose which scenes from Suzanne Collins's book would fit into the big-screen adaptation.
On not including the moment Katniss Everdeen (Jennifer Lawrence) meets an Avox, Ross told MTV News: "It was just that there was no room for that in the storytelling, unfortunately.
"The William Faulkner line is, 'You have to kill your darlings'. That was one that unfortunately fell by the wayside. I was sorry about it."
The director went on to say that he did add certain scenes to the film that had not appeared in the book, including a riot scene following Rue's death.
"I thought it was important that you begin to start to make the turn into Catching Fire, that you see the seeds of the rebellion, you see what Katniss has caused," Ross said.
The Hunger Games opens in cinemas on March 23.
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Watch Digital Spy talk to the stars of The Hunger Games below: