The towering defender has been absent for the Bees' last two games with a foot problem, but he is now back on the training pitches and is on track to play a part in Monday's game.
Ajer's return would leave Brentford only missing their five long-term victims in Aaron Hickey (thigh), Gustavo Nunes (back), Igor Thiago (knee), Josh Dasilva (knee) and Rico Henry (knee), the latter of whom is not being risked just yet despite entering the final stages of his recovery.
Should Ajer be given the thumbs-up to start the derby, Sepp van den Berg should switch across to the right-hand side of the four-man rearguard, in turn demoting Mads Roerslev to the bench.
Ethan Pinnock and Nathan Collins are poised to form an unaltered central pairing in front of Mark Flekken, while Christian Norgaard and Vitaly Janelt should act as the double pivot just in front of the defence.
Back to his creative best in the 2024-25 season, Mikkel Damsgaard will once again be floating in and around the number 10 role, no doubt supporting Bryan Mbeumo, Yoane Wissa and potentially Keane Lewis-Potter up top.
Responsible for two goals in the thrilling 4-3 win over Ipswich Town, Mbeumo already has eight efforts to show from nine outings in 2024-25, while Wissa scored his ninth goal in 10 top-flight starts against the Tractor Boys.
Brentford possible starting lineup:
Flekken; Van den Berg, Collins, Pinnock, Ajer; Damsgaard, Janelt, Norgaard; Mbeumo, Wissa, Lewis-Potter