With one game left, Group G has Lille with 8 points, Salzburg with 7 points, Sevilla with 6 points, and Wolfsburg with 5 points. Lille can't finish last, Wolfsburg can't finish first, and the middle two can finish anywhere. Wolfsburg hosts Lille, and Salzburg hosts Sevilla. If both games are draws, first and last will finish 3 points behind. I checked the last ten complete seasons, which had 80 groups, and the least difference between first and last was 4, which was done four times, including iin 2011-2012 when APOEL Nicosia of Cyprus won their group and reached the Quarterfinals.
Three point difference has happened four times in the past. 2000-01 - Group D Sturm Graz ...... 10 points Galatasaray ....... 8 Rangers ............. 8 Monaco .............. 7 https://en.wikipedia.org/wiki/2000–01_UEFA_Champions_League_first_group_stage#Group_D 2001-02 - Second Group Stage, Group D Bayer Leverkusen ......... 10 points Deportivo La Coruña ..... 10 Arsenal ............................ 7 Juventus .......................... 7 https://en.wikipedia.org/wiki/2001–02_UEFA_Champions_League_second_group_stage#Group_D 2003-04 - Group A Lyon ...................... 10 points Bayern Munich ....... 9 Celtic ...................... 7 Anderlecht .............. 7 https://en.wikipedia.org/wiki/2003–04_UEFA_Champions_League_group_stage#Group_A 2003-04 - Group B Arsenal .................... 10 points Lokomotiv Moscow ... 8 Internazionale ........... 8 Dynamo Kyiv ............ 7 https://en.wikipedia.org/wiki/2003–04_UEFA_Champions_League_group_stage#Group_B But there was one instance where the gap between first and last was just 2 points: 1998-99 - Group B Juventus ............. 8 points Galatasaray ........ 8 Rosenborg .......... 8 Athletic Bilbao ..... 6 https://en.wikipedia.org/wiki/1998–99_UEFA_Champions_League_group_stage#Group_B