Arsenal manager Mikel Arteta says he is "pretty worried" about Bukayo Saka after the England winger went off injured against Crystal Palace.
Saka suffered a hamstring injury during Saturday's 5-1 win at Crystal Palace and had to be replaced in the 24th minute.
The 23-year-old was using crutches as he left Selhurst Park.
"He felt something in his hamstring, he couldn't continue," said Arteta. "He will have to be assessed. [I'm] pretty worried about that one."
Asked how long Saka might be out, Arteta replied: "It's difficult. They have tested him but it's very difficult to say how bad it is.