The 'Radioactive' group's fifth studio record Come Around Sundown was released on Monday and is tipped to reach the number one spot this weekend.
However, Followill suggested that the ex-Britain's Got Talent singer, who releases The Gift on November 8, will be too popular to defeat.
He told The Sun: "I am worried about Susan Boyle. If she sells more records than us. She is a force of nature, that woman."
Of their new album's chart prospects, the singer added: "I am anxious to see how our album does now it's out in the UK. I usually don't think about it but the day before I start to think too much."
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