The Dutch defender sustained a knee injury in Arsenal’s Premier League opener against Nottingham Forest.
Timber will go under the knife and could be unavailable for a significant period of time.
The defender who just arrived this summer felt no immediate pain and underwent stringent tests during the interval.
His long-term injury was a blow to Mikel Arteta and club fans who were excited to see him in action in the new campaign.
Kieran Tierney who was expected to leave Emirates this summer could now be retained for the season.
But Mikel Arteta didn’t rule out doing more business in the transfer window.
Arteta said: “Huge blow. Especially for him after just joining the club. To have the injury he has is a huge blow.
“He’s been very good to be honest. He’s a special character. He knows, he’s starting to realise the extent of the injury and the amount of time he’s going to be out. But he’s in a good place. We are willing to help him obviously and be close to him, but we know it’s going to be a long journey.”
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