"We were a bit jaded against Valencia while our opponents had more pace than us," Belfodil told Inter Channel.
"We're disappointed, of course, because we always want to win, but the most important thing in this period is that we keep on improving.
"We were more tired than Valencia and it was pretty clear out there, but at this stage of the season fitness levels come into it a lot and whichever team has got more in them wins.
"There's nothing wrong with our preparation. It doesn't matter whether our work pays off immediately or not. What matters is being ready for when the matches mean something."