Demi Lovato Dinner Date with Neymar ... Just Friends?

Is Demi Lovato in the "friend zone" with Neymar?

The singer and the soccer superstar went for a dinner date in London on Tuesday -- after Neymar played for Team Brazil in an international friendly against England.

Oh, there was a 3rd person at the dinner as well ... smokin' hot TV host Layla Anna-Lee.

But despite the fact Neymar and Demi look GREAT together, the soccer stud is preemptively striking against dating rumors ... posting Instagram photos with the caption, "My friends girls."

BOOOOO!!!!