Celtic, who have racked up seven points from five games including a memorable 2-1 victory over Barcelona, will secure their place in the knockout rounds if they can better Benfica's result.
"It would be my best achievement as a manager here," said Lennon.
"It would be great for everyone associated with the club and it would give the players something to look forward to and get their teeth into in the new year.
"No one gave us a prayer coming into the competition.
"There were people saying we wouldn't get a point and people saying we wouldn't get into the Europa League but we felt that we had a decent chance and that's what we have given ourselves.
"However, regardless of the outcome, we will have European football in the new year and that was one of the targets going into the group.
"Which competition it is in remains to be seen but we would all love to be in the Champions League, obviously."