Arsenal centre-half Rob Holding has ruptured the anterior cruciate ligament in his left knee and has been ruled out for the rest of the season.
Holding was forced off in the first half of the Gunners' 2-2 draw with Manchester United on Wednesday after a challenge from Marcus Rashford and was replaced by Stephan Lichtsteiner.
And Arsenal's official website have confirmed that the Englishman's campaign is over following a serious knee injury, with the rehabilitation process expected to take between six and nine months.
"Further to the injury sustained during our match at Manchester United on Wednesday night, we can confirm that Rob Holding has ruptured the anterior cruciate ligament of his left knee," a statement read.
"Rob will undergo surgery to repair this in the coming days. The rehabilitation process is expected to take between six to nine months.
"Everyone at the club will now be working as hard as we can to ensure Rob is back on the pitch as soon as possible.
Next Match
Arsenal host Huddersfield Town on Saturday with just two fully fit senior centre-backs in Sokratis Papastathopoulos and Skhodran Mustafi, while Laurent Koscielny is on the verge of a well-timed first-team return. Kostantinos Mavropanos has also out been out injured with a groin strain.
Arsenal boss Unai Emery has taken to employing three central defenders, and did so in the Gunners' last three Premier League matches against Bournemouth, Tottenham and Man Utd, but the absence of Holding for the entirety of the season may see him revert to the 4-2-3-1 utilised for the vast majority of the campaign thus far.
Alternatively, he may opt to use Lichtsteiner as the right-sided centre-back - as was the case at Old Trafford - to plug the gap until the likes of Koscielny, Mavropanos and Nacho Monreal return to provide more suitable options.
Despite Arsenal's recent form - they are on a 20-game unbeaten run in all competitions - defence has been a notable area of weakness this season. In fact, they have kept just two Premier League clean sheets all season, in 2-0 victories over Everton and Watford.
As a result, Holding's injury and the relative age of the returning Koscielny at 33, as well as the erratic form of Mustafi and Sokratis thus far could force Emery to dip into the transfer market in January and seek a replacement.
However, if a suitable option cannot be found, Arsenal have Calum Chambers out on loan at Fulham and could simply look to recall him rather than purchasing a new player just for the sake of it.