The Premier League club defeated Club Brugge 3-1 at Old Trafford in the play-off first leg last week which has them well-positioned to move through to the group stage proper of Europe's premier club competition.
The return leg takes place in Belgium on Wednesday night and United midfielder Fellaini, show scored the third goal last week, is feeling assured.
"At the moment we are doing well," said the Belgium international.
"We don't concede and we can score. We have a lot of quality in the team - we can do well in the Champions League."