Group winners will be drawn against group runners-up, and clubs will not be drawn against others from the same country, nor against those they have already faced in the group stages.
ARSENAL & MANCHESTER CITY
Potential opponents: Atletico Madrid, Barcelona, Bayern Munich (Arsenal only), Borussia Dortmund (Man City only), Real Madrid, Paris St Germain.
It is hard to suggest there is a favourable draw to be had from this group, although Spanish superpowers Barcelona and Real Madrid perhaps stand out as the ones to avoid thanks to their dazzling array of superstar names.
The same might also go for the German sides, but the fact City beat Bayern and Arsenal topped Dortmund on their travels during the group stages would at least offer hope.
Atletico do not hold the same fear factor as the other La Liga sides, but cannot be taken lightly as they sit joint-top of the table alongside Barca, three points clear of neighbours Real, and also came through Group G unbeaten.
The prospect of facing PSG front pair Zlatan Ibrahimovic and Edinson Cavani hardly appeals either.
CHELSEA & MANCHESTER UNITED
AC Milan, Bayer Leverkusen (Chelsea only), Galatasaray, Olympiacos, Schalke (Man Utd only), Zenit St Petersburg.
To see why Arsenal's loss in Napoli and City's failure to snatch a fourth goal in Munich could prove so costly, you need only compare this second group to the the first.
While Chelsea and United will not want to underestimate the likes of AC Milan and Schalke, indifferent domestic form does little to inspire trepidation and both showed their vulnerabilities in the group stages, Schalke were comprehensively beaten by Chelsea home and away while Milan played out several draws.
Galatasaray have improved under former City boss Roberto Mancini, but Jose Mourinho and David Moyes would no doubt have been happy to see them secure progression ahead of Juventus.