Arsene Wenger has confirmed Alexis Sanchez faces an extended spell on the sidelines.
After returning to training at the weekend, Alexis Sanchez was a surprise absentee from Arsenal's squad to take on Manchester City last night.
While his presence in the starting line-up was always a doubt, it had remained possible that he would be on the bench as he sought to recover from a hamstring injury.
Speaking to Arsenal.com after the game, manager Arsene Wenger confirmed that the Chile international had suffered a setback in training.
He said: "I think he will be back January 10. Christmas period - you can’t count him.
"He had had a slight one (setback) yet but he planned to be on the bench tonight but he is so keen he got a little bit of a pain and we didn’t take a gamble."
Wenger added that Sanchez suffered the set back two days ago.
The forward is always keen to play, and this has proved difficult for Wenger to manage, originally suffering the injury amid fears of burnout, but having insisted he was fit enough to feature.
Out for Christmas
If Wenger's projected comeback date is accurate - a big if based on previous predictions - Sanchez will miss four games.
These include three Premier League games and one FA Cup match.
In the league he will be out for the Boxing Day visit to Southampton, at home to Bournemouth, and at home to Newcastle. He will also be out for the cup game at The Emirates against Sunderland.
Sanchez's return game would potentially be on January 13, away to Liverpool at Anfield in the Premier League.