Jurrien Timber has suffered an anterior cruciate ligament injury to his right knee and will undergo surgery in the coming days, Arsenal have confirmed.
Timber, 22, limped off the pitch in the 50th minute of the Gunners’ 2-1 victory against Nottingham Forest on Saturday.
The Netherlands international signed from Ajax for £34m last month.
In a statement, Arsenal said Timber “will be out of action for a period of time” without specifying a duration.
The club added: “The support and expertise from our medical team and everyone at the club will now be focussed on Jurrien’s rehabilitation programme, to ensure he recovers well and is back playing as soon as possible.”
Timber made his debut for the Gunners in the Community Shield victory against Manchester City before the season opener with Forest, during which Mikel Arteta had to send on Takehiro Tomiyasu in the second half after the versatile Dutch defender signalled he could not go on.
He made 47 appearances in all competitions for Ajax last season, including all six of their games in the Champions League group stage, and helped them win the Eredivisie title in 2021 and 2022.
Arsenal, who finished in the Premier League last season, are next in action against Crystal Palace at Selhurst Park on 21 August.
Timber is the latest player to suffer a major injury at the start of the new campaign.
On Tuesday, City manager Pep Guardiola said midfielder Kevin de Bruyne will miss up to four months of the season and the club will decide whether he needs surgery on a hamstring injury.
The 32-year-old Belgium international hobbled off after 23 minutes in City’s opening win against Burnley at Turf Moor on Friday.
Meanwhile, Aston Villa have lost two players to long-term injuries.
Argentina midfielder Emi Buendia could be out for up to eight months with a knee ligament injury he sustained in training before the season started, while defender Tyrone Mings was then stretchered off during their opening 5-1 defeat by Newcastle United after he suffered a knee injury that requires surgery.