Manchester United star Alexis Sanchez is set for a spell on the sidelines after it was confirmed he has suffered a hamstring injury.
The Chilean has started just seven matches so far this season in a campaign that has been plagued by injuries.
Speaking to the press on Friday, manager Jose Mourinho confirmed the injury and was not confident of the attacker's chances of featuring again before the new year.
"The first thing I can say is that in every club, when a player is not playing it is a simple manager’s decision," the Old Trafford boss said.
"In our club, when a player does not play, it is always because the player is not behaving and has disciplinary issues. Of course that is not the case again.
"He has an important injury, I don’t want to risk by saying for how long he will be out but from the top of my experience I would say he is not playing this year.
"No scans yet. But the player is experienced, the player knows what the injury is and also from the top of my experience, just the painful scream and the way the injury happened I know it’s going to be for a long time.
"It's not a little muscular injury that in one week or 10 days the player is ready, is for me and also for Alexis, the feelings before the scans is that the grade is different than the Lindelof one and the Lindelof one was not an easy one, so I think Alexis has what I used to call an aggressive muscular injury."
Having missed out on a place in the matchday squad for United's win against Young Boys on Tuesday, Alexis was expected to be required again during the upcoming festive schedule.
Mourinho's side are to travel to the south coast to take on Southampton in their next match this Saturday, before they host Arsenal and Fulham in the space of three days next week.
They are also due to wrap up their Champions League group stage fixtures with an away tie at Valencia next month, before they travel to Anfield to take on Liverpool.
Mourinho was quizzed on Alexis' omission during the win over Young Boys earlier this week, where he confirmed that the former Barcelona and Arsenal forward was not injured at the time.
"No he is not injured, but it is quite curious because you always speak about the ones who are not playing," the United boss said following the match.
"Today (on Tuesday) you had (Marcus) Rashford as a 9, that's what you want, what you ask all the time, it's what you had."
Alexis has just one goal to his name so far this season having lost his place in the side during the early stages of the campaign.
There has been speculation that the 29-year-old is unhappy with life in Manchester having joined the Red Devils from Arsenal in January.
The form of Anthony Martial will have played a part in Alexis' lack of opportunities in recent weeks, with the Frenchman netting six league goals since the start of October.
Altogether, Alexis has managed just four goals in 30 appearances for United, having notched 80 in 166 for the Gunners.