Arsenal manager Arsene Wenger confirms midfielder Aaron Ramsey will be out of action for at least two weeks.
The Frenchman described the 24-year-old's injury as a worrying one after the 2-1 victory over Leicester City in the Premier League.
And on Friday, Wenger explained that the player is expected to be sidelined for two weeks, hence missing games against Middlesbrough, Crystal Palace and also Monaco in the Champions League.
"Aaron Ramsey will be out [for maybe two weeks] yes, he has a little hamstring strain," Wenger told reporters.
"We haven't found [his] underlying reason, there is an underlying reason that is certainly medical or bio-mechanical because he is a guy who is serious, works hard, has a controlled and disciplined life, so there's no obvious reason why he should have muscular problems."
Asked to give a full update on all other injured players, Wenger said: "Alexis [Sanchez] is still not able to go out, he could be short again for Sunday.
"Jack Wilshere's back in normal training but has been out for [more than two] months and misses competition.
"He worked very hard and is focused, committed, but it will take him a while to get back to competitive level. He's motivated and focused to come back as quickly as possible.
"He worked very hard but he has still been out for [more than two] months and what he needs now is to get back.
"Competition gives you that sharpness that training cannot give you because it's about a combination of fitness and decision-making - and speed of decision-making. It takes a while to get that back."
