The Cottagers have recorded just two points from five games at the second tier, and Jokanovic has acknowledged that his players must improve in order to remain away from the relegation zone.
The 49-year-old told BBC Sport: "We did not show enough quality. We need to adapt better to the competition. I have tried to find some solution with better options.
"The past four games we have only one point. Not good news. For a month now, we have not been at the right level.
"We must fight all together and show more quality. If not, then we are in trouble."
Fulham are next in action when they host Derby County after the international break.