Maurizio Sarri's side have only picked up a point from their last two games after 4-2 loss to Roma a fortnight ago.
With Napoli now trailing Juventus who still have an outstanding match by a point, Koulibaly rued his side’s inability to break the deadlock against Luciano Spalletti’s men.
And the Senegal international who has played in all but one league match this season, is not giving up on the Light Blues’ chances of winning their first Serie A title since 1989-90 season
“It’s a pity about [Sunday's] result, because we played well and only lacked a goal,” Koulibaly told Radio KissKiss.
“We are on the right track and just have to continue our path. Anyone who doesn’t believe won’t stay in our locker room, as there’s a long way to go. Anything can happen and we just need to stay up there.
“All Inter did was chase after the ball. It’s disappointing, because we played well, but we must believe to the end. Nothing changes as far as I am concerned, there’s a long way to go and we must pick up as many points as possible.”
Napoli, placed second with 70 points from 28 matches so far, welcome Genoa to the Stadio San Paolo for the next league fixture on MArch 18.