Lohan recently posted a photo on Instagram of herself with George.
Asked by a fan online if he had moved on from his ex-girlfriend, Michelle Keegan, and is now dating Lohan, George tweeted, "Nooooooo."
"If you date with Lindsay, I will die okay," another admirer tweeted to George.
"I'm not, so you're fine!" he replied.
"Rumours...That's all...," he added. "Like I said...1million %."
George admitted to E! News the troubled former child actress occasionally hangs out with his boy band, but stressed none of its members are seriously involved with her.
"She was good to party with, but there's definitely not going to be any babies on the horizon," George told E! News.