Arsenal manager Mikel Arteta admitted he was "pretty worried" over an injury suffered by star winger Bukayo Saka in Saturday's 5-1 win over Crystal Palace.
Saka, who was forced off midway through the first half, was seen on crutches leaving Selhurst Park after a game which saw the Gunners move to within three points of Premier League leaders Liverpool.
"He (Saka) felt something in his hamstring," Arteta said.
"He couldn't continue. He will have to be assessed, so I'm pretty worried about that one.
"It's very difficult to give a prognosis now. They have tested him inside but it's very difficult to say how bad it is."
He added: "Unfortunately with the amount of games that we are playing, every three days with this schedule, it doesn't surprise me, but the team will react to that."
Arsenal next face struggling Ipswich on Friday, Brentford on New Year's Day and Brighton just three days later in the holiday fixture programme.
AFP