Welsh International Aaron Ramsey is out for the remainder of the festive period after he picked up a thigh strain in Arsenal's 3-1 win over West ham at Upton Park.
The midfielder was subbed off after an hour.
The Hammers had taken the lead through Carlton Cole, and it was still 1-0 as Ramsey was replaced by Lukas Podolski who set up Theo Walcott for his second and then added a third for Arsenal.
But the Gunners will certainly miss Ramsey who is having his best year in the Premier League with 13 goals in 27 appearances in all competitions.
"It looks [bad], it looks a thigh strain," said Wenger. "The Christmas period is certainly over for him.
"I don't know how long it will be, we have to see tomorrow morning."