Arsenal may be three points clear at the top of the group, but still they can be eliminated in a fortnight's time.
A Dortmund win at Marseille, and Napoli winning by three clear goals, will see them drop into the Europa League instead. Unthinkable, right?
Laurent Koscielny and Olivier Giroud will know the danger, seeing their France side achieve a similar last gasp fightback against Ukraine.
The San Paolo is a stadium where Chelsea were turned over not so long ago, 3-1 in 2012, swap the Edinson Cavani and Ezequiel Lavezzi of that night for Gonzalo Higuain and top prospect Lorenzo Insigne.
The Napoli frontman has warned Arsenal they are in for a tough battle.
After their loss to Dortmund he told Mediaset Premium: "The last race we will try to give everything to win and go through.
"The fans will give us a hand because at the San Paolo is not easy for anyone, we will give the maximum for all 90 minutes."
It will certainly be a tough challenge for the Gunners, but a character building one at that. A lot has been said about the new resilient character of this Arsenal side, 90 minutes in Napoli will be the acid test.
image: © ell-r-brown