Arsenal coach Unai Emery has admitted that the club may need to bring in a centre-back in January to boost his defensive options.
Arsenal are facing a shortage of defenders after Rob Holding was ruled out for the season last week with a torn knee ligament, while Laurent Koscielny is only now ready to play his first game of the campaign after recovering from an Achilles injury.
But with doubts remaining over whether Koscielny can be fully relied upon at the age of 33 after seven months out, Emery said he would ideally find reinforcements in January.
"If we can take one player to help us at centre-back, I think it's a good option," Emery said. "But a transfer is not easy."
Sources have told ESPN FC that Arsenal have identified Manchester United's Eric Bailly and Chelsea veteran Gary Cahill as potential January replacements for Holding.
It remains to be seen how quickly the 33-year-old Koscielny can get back to his best after nearly seven months on the sidelines, while Konstantinos Mavropanos, 21, is still out with a troublesome groin injury and hasn't played all season.
That leaves Emery with just Sokratis Papastathopoulos and Shkodran Mustafi as his senior centre-back options -- but both those players are suspended for Sunday's trip to Southampton.
Koscielny is set to start in Thursday's Europa League game against Qarabag and Emery said he will decide after that whether the Frenchman is ready to play in the Premier League this weekend.
"We are going to look also if he can play 90 minutes or less minutes in this game [against Qarabag]," Emery said. "Koscielny is coming back and for the team it's very important he is coming back and then we are going to wait and see how Mavropanos is improving with his injuries, because he is also a centre-back who can help us.
"Another option [is] we can play with two, with three [centre-backs], Nacho Monreal and Stephan Lichtsteiner can play in this position. I prefer to use, if we can, a [natural] centre-back."
Academy product Zech Medley could also get his first start against Qarabag, although Emery said he has yet to decide whether to play a back three again or revert to a back four.
"We need to use different options. We can do a big performance with the two formations in each game," he said.
"Tomorrow maybe we can start with four and finish with three. For the next matches the same because for example in the last match against Huddersfield we started with three centre-backs and then we finished the second half with two.
"It depends, also, how we are with the players and how we can take our performance better with the two different ideas."