The 24-year-old has recently been linked with a move to Tottenham.
Dembele fears he must leave the Cottagers if Fulham fail to match his ambition.
Dembele said: “I’m not concerned about losing time here, but it’s clear that I’d like to play at a higher level.
“Spurs were interested but I can’t talk about other clubs. I’m ambitious and would like to play for a club in the top five.
“It’s hard to say what is stopping Fulham from progressing. We have good players and I feel we’re better than all the clubs except for the Big Four, and Manchester City.
“But each season we change our coach which makes it difficult.”
