The chance is still there, but it's very slim, this season there are several teams that have managed to add to the competition in the top four positions. Arsenal and Newcastle have enlivened the competition with impressive performances shown since the start of the season, Arsenal managed to sit in first place by breaking the dominance of Manchester City. Meanwhile, Newcastle have appeared extraordinary this season which has made them successful in third place.
Tottenham, Manchester United, Liverpool and Brighton are above Chelsea, there is still a lot for Chelsea to do to get into the top four. Potter has not been able to fulfill the hopes of Chelsea's owners, defeats in the last few matches have made Chelsea slump to eighth place. It took a consistent struggle for Chelsea to get past several teams that were above it, with the more teams that occupy the top four positions the less chance Chelsea have to re-enter the UCL zone.
Chelsea improved after Potter was appointed as coach, but in fact Potter cannot be immediately expected to be able to make Chelsea appear consistent and win all the matches they play. That's a tough expectation for any coach, but let the process take its course and see how the team gets back on track after the coach and his staff evaluate his team.
I don't think Chelsea are starting to lose hope of ending this season in the Champions League zone. Even if their recent form has been lacking, there are plenty of opportunities to improve after the World Cup break. Chelsea is a good team, but the tough competition in the Premier League will never be easy for any team to reach their final target.