The 'Bleeding Love' singer was rumoured to be duetting with Adele at the Olympic stadium, but told the Daily Star that the reports are "unfortunately... not true".
"I'm not performing there, with or without Adele," she told the paper prior to taking the stage at Radio 1's Hackney Weekend.
"I would obviously love to, though. She's incredible."
Lewis plans to release her third album, titled Glassheart, this October. Lead single 'Trouble', written by Emeli Sandé, is due to go on sale shortly before.
Speaking about the multiple delays to the album's release, Lewis said that it had taken so long to finalise because she wanted it to be "a classic".
"All the songs are strong," she explained. "There will be no fillers.
"I'm so proud of it. It has a dark edge and even has a bit of dubstep in it. I just want my fans to hear it now."
Watch the video for Leona Lewis's 'Bleeding Love' below: