Mikel Arteta said Arsenal are "actively looking" for a replacement for the injured Mikel Merino in the closing hours of the transfer window.
Merino, who has been a valuable contributor in midfield and attack for the Gunners, could miss the rest of the season with a fractured right foot that requires surgery.
Arteta stressed how significant the Spain international's absence as Arsenal compete to win four trophies.
The Arsenal boss hopes his club can come up with a new signing to fill the void before Monday's 1900GMT deadline.
"We are actively looking at options and we will continue to do that," Arteta told reporters on Monday.
"When you lose a big player like this with four months to go, and all the competitions to play for, you need to look and we need to do everything we possibly can to see if a player is available."
The loss of Merino has been tempered by the return to fitness of Germany forward Kai Havertz.
There was further good news for Arsenal as Arteta revealed an injury that kept England winger Bukayo Saka out of Saturday's 4-0 win over Leeds is only minor.
"Today, he (Saka) was better. Let's see how he responds. It doesn't look like something too serious," Arteta added ahead of Tuesday's League Cup semifinal second leg against Chelsea
"Whether he is available for tomorrow or the weekend, we will have to wait and see."
Arsenal remain on course for an unprecedented quadruple.
Arteta's side hold a six-point lead at the top of the Premier League, have progressed to the last 16 of the Champions League and face third-tier Wigan in the FA Cup fourth round.
But the Spaniard is focused on reaching the League Cup final as his side's first opportunity to end a six-year trophy drought.
Arsenal hold a 3-2 lead over Chelsea ahead of the second leg on home soil at the Emirates Stadium.
"The next one is always the most important one. And it is the closest, at least, to reach a final," said Arteta.
"We really need to create the atmosphere, the energy, the belief that we're going to do it."