Arsenal fear Calum Chambers could miss the rest of the season with a serious knee injury.
Chambers limped off during Sunday’s defeat against Chelsea and Gunners medics feared the worst following initial tests.
The defender underwent a series of tests on Monday and there are growing concerns he has suffered damage to his anterior cruciate ligament.
Chambers has been a rare bright spot for Arsenal during what has been a hugely disappointing season and his injury comes as a significant blow to new boss Mikel Arteta.
The news will see Arsenal ramp up their search for a new central defender when the transfer window reopens on Wednesday.
Sportsmail revealed on Monday how Arsenal will provide newly-appointed manager Arteta with transfer funds next month to plug their leaky defence.
Money is limited following three seasons without Champions League football, but the club will back Arteta with cash when the January window reopens – with the Gunners prioritising a centre back.
Red Bull Leipzig’s Dayot Upamecano is high on the list of the club’s central defensive targets and the German side could be persuaded to let him leave due to the fact his contract expiring. He could be available for as little as £40million.
The Gunners had a concrete interest in Upmecano, who has 18 months left on his deal, in the summer but felt his price was too high.
But with much of the ground work done regarding a move for the 21-year-old, Arsenal are well-placed to strike.
Their need for a new centre back next month was exacerbated on Sunday following a knee injury to Chambers against Chelsea on Sunday.
Arsenal medics were pessimistic about Chambers’ injury on Sunday night but the club were on Monday trying to ascertain if the defender has sustained significant ligament damage.