Walcott limped off in the 60th minute at the Emirates Stadium and Gunners manager Arsene Wenger revealed he does not expect the England international to feature in Arsenal's final three Premier League matches.
"It looks like a serious hamstring," Wenger said. "When we first assessed the hamstring, he wanted to stay on the pitch, and I think he should have gone off straight away because the second time it was a real hamstring injury.
"I think now for him it will be tough to come back before the end of the season. It is usually 21 days minimum. He should be OK to play for England, but I don't think he will be ready to play for us."