Arsenal great Martin Keown insists that his old side must dip into the transfer market after an ankle injury to Shkodran Mustafi at Bournemouth.
The Gunners started the game brightly and led 2-0 at the break thanks to goals from Bukayo Saka and Eddie Nketiah.
But the Gunners lost centre-back Mustafi to injury during the contest, meaning their depth will once again be tested.
Mikel Arteta is already without Calum Chambers due to a knee problem and Keown now believes that Arsenal must make an important transfer decision.
"They have lost Mustafi tonight and you'd have to say it looks like a really bad one. That will force them into the transfer market," Keown told BT Sport. "Numerically Arsenal need a centre-back. There is so much to fight for.
"But these young men should be proud of their efforts. They had quality, imagination and they showed desire."
Whilst Arsenal were impressive in the first half, it was a tough second period for the visitors.
Bournemouth were more dominant and halved the deficit thanks to Sam Surridge's goal in the fourth minute of stoppage time.
Arsenal, though, held on and booked their place in the fifth round of the FA Cup, where they will face Portsmouth away from home.
