Arsene Wenger admits he may have to dip into the transfer market depending on the severity of Arsenal defender Sebastien Squillaci's injury.
Squillaci suffered a hamstring injury during Saturday's FA Cup third round draw with Leeds United and is waiting to learn the extent of the damage.
The Frenchman joins Thomas Vermaelen on the sidelines and a lengthy spell out of action for Squillaci could force Wenger's hand.
The Gunners face Ipswich Town in the first leg of the Carling Cup semi-final on Wednesday, with Laurent Koscielny and Johan Djourou the only fit centre-halves available to Wenger.
The Arsenal boss is aware he can not manage with only two options and is ready to bring in a new defender once he learns how long he will be without Squillaci.
"If we only have two centre-backs then that cannot work with the number of centre-backs we have," said Wenger.
"If Squillaci has a problem then we must quickly go out for a player."
Bolton Wanderers defender Gary Cahill has been linked with a move to Emirates Stadium, while the veteran Sol Campbell has been tipped for a third spell with the club.