Arsenal boss Arsene Wenger says the Gunners are still on lookout for reinforcements ahead of the new Premier League season.
The Emirates club have been linked with a number of players across Europe this summer, including striker Alexandre Lacazette and Leicester's PFA Player of the Year Riyad Mahrez.
However, the Gunners are desperately in need of defensive cover, following Gabriel's injury against Manchester City, and Wenger admits he is hoping to add to his squad before the close of the window on August 31.
"We are in the transfer market, but we are focused on concentrating on our players - we have to get them ready for the season", said Wenger at the launch of the new Premier League season on Wednesday.
"On the other hand, with what happened with us, of course we are looking outside to strengthen our squad."
Arsenal have been heavily linked with a move for Valencia centre-half Shkodran Mustafi and the two clubs are believed to be currently holding talks over the 24-year-old's future.
Mustafi has a release clause of £42.1m in his contract at the Mestalla but Arsenal may be able to sign the German for £25.3m, plus a further £8.4m in add-ons.
The Germany international, who featured for Joachim Low's side at Euro 2016, has been left out of Valencia's squad for Wednesday's pre-season friendly against Nigeria All-Stars.
The Gunners face Liverpool in their opening game of the season on Sunday with no senior centre-backs available for selection.
Per Mertesacker has been ruled out of the start of the campaign with a long-term knee injury, while first-choice centre-half Laurent Koscielny is yet to return to club duty after reaching the final of Euro 2016 with hosts France.
And with Gabriel now sidelined, Wenger may have to turn to an inexperienced pairing of Calum Chambers and Rob Holding for the match against Jurgen Klopp's Reds.
Gunners midfielder Jack Wilshere acknowledged the club's dire need for defensive cover but believes Wenger's side possess enough attacking talent to take all three points on Sunday.
"We picked up a few injuries in defence so we probably need to get a defender in," he said.
"But even then we brought in Rob Holding, who has done great in pre-season, and we have got another young centre back in Calum Chambers and going forward we are one of the best teams in the league."