Arsenal midfielder Tomas Rosicky, who had just returned from an 18-month injury layoff, could be sidelined for six weeks with a hamstring problem, the Premier League club said on Friday.
The Czech Republic international, who played in three pre-season friendlies in recent weeks after recovering from a hamstring tendon injury, will miss the start of the season and manager Arsene Wenger admitted the new injury was worrying.
"He was so sharp that it is difficult to accept that he has had a muscle injury," Wenger was quoted as saying on the club's website.
"But it is not a major problem. You get that type of injury after you have been out for 18 months."