In the influential midfielders were both injured during the trip to Anderlecht in the previous round of group games; Armstrong picked up a strain in training while Brown was substituted off with a hamstring injury during the 3-0 win.
Elsewhere, Mikael Lustig is preferred to Nir Bitton at centre-back with Jozo Simunovic failing to prove his fitness in time. That opens up a space for Cristian Gambos to start at right-back.
In attack, Leigh Griffiths gets the nod ahead of French striker Moussa Dembele.
Celtic XI: Gordon; Gamboa, Lustig, Boyata, Tierney; Brown, Ntcham, Armstrong, Roberts; Sinclair, Griffiths
Subs: de Vries, Bitton, Dembele, Rogic, Ajer, McGregor, Forrest