Arsenal midfielder Aaron Ramsey will miss the rest of the club's holiday fixtures after hobbling off with a muscle injury in the 3-1 victory at West Ham United on Thursday.
Ramsey, whose eight league goals this season have helped the Gunners to the top of the table, appeared to injure his thigh in the 65th minute and was replaced by Lukas Podolski whose goal sealed a comeback victory.
"It looks (serious)," Wenger told a news conference.
"It looks like a thigh strain. I don't know how serious the thigh strain is but the Christmas period certainly is over for him. It was his birthday today."
"I don't know how long. We will see tomorrow morning," Wenger said when asked how long the Welshman would be out for.
Theo Walcott's double helped turn the match in Arsenal's favour after Carlton Cole had given West Ham the lead shortly after halftime and meant Arsenal avoided a fourth league match in succession without victory.
"When you do not win for four games it's important to come back for the confidence level of your environment and yourself as well to win," Wenger said.
"For us we have another good game now on Sunday at Newcastle who are in full confidence as well so that will be another test.
"The team wants to do well and the character is great. The concentration is top. I believe we had a difficult period just now but honestly that was mainly down to the schedule we had.
"I think that the schedule was absolutely horrendous."
Podolski's return from a hamstring injury that had sidelined him since August was a boost for Wenger's title- chasers.
"He has been out for four months, he has not played one game. I try to get him slowly back to competitiveness and he has shown he can have a huge impact because he can score and make goals," Wenger said.
Arsenal are away at sixth-placed Newcastle on Sunday, then host Cardiff City on New Year's Day before a tasty FA Cup third-round tie against north London rivals Tottenham Hotspur.