Right-back Bellerin could be unavailable until the new year after sustaining a suspected calf issue shortly before half-time in the 3-2 defeat at St Mary's.
Emery described the problem as "small" but expects his Spanish compatriot to have "some weeks off" in another blow to a backline which lost Sead Kolasinac to thigh tightness before Sunday's match.
Rob Holding is already out for the season and Konstantinos Mavropanos has not been sighted this term, while Laurent Koscielny appeared well off the pace in his first Premier League start since April.
Shkodran Mustafi and Sokratis Papastathopoulos have, however, served their one-game Premier League suspensions and Emery may have to make do without further reinforcements.
"I don't know now because we don't have a lot of possibilities in January, but maybe we can think of someone to sign to help us," the Gunners boss told reporters.
"[But] only if we think they are the player that can give us good performance. It's not easy. I don't believe a lot in this transfer window because it's not a big possibility with players.
"The club is working and only if some player can help us with a high level [will we make a signing]."
August 25th - December 15th: WWWWWWWWWWWDWDDDWWWDWW
Our unbeaten run may have ended today, but we go again on Wednesday
Back to home, back to work #WeAreTheArsenal pic.twitter.com/Ncnu15hANi — Arsenal FC (@Arsenal) December 16, 2018
It was hoped the experienced Koscielny, recently recovered from a long-term Achilles injury, would add strength to a makeshift three-man defence against Saints, but his marking was persistently poor as Danny Ings notched two first-half headers before Charlie Austin nodded in an 85th-minute winner.
Emery defended the former France international and insisted his unconvincing combination with Granit Xhaka and Stephan Lichtsteiner was not to blame for the end of Arsenal's 22-game unbeaten run, which came despite Henrikh Mkhitaryan's double.
"I think today is very good news for Koscielny, physically he can play this match 90 minutes. Xhaka played well and Lichtsteiner played well," the Spaniard said.
"We conceded chances today but we also had more chances to score than the two goals. The difference is this. Our game today was similar to what we played before, but the result was different."