Ching left the Dynamo's home opener against Real Salt Lake on Thursday night because of the strain.
The 31-year-old from Hawaii made his national team debut in 2003 and has 11 goals in 44 international appearances. He was on the 2006 U.S. World Cup roster but didn't play during the tournament.
With Sochaux's Charlie Davies still sidelined because of severe injuries sustained in an October car crash, the U.S. is uncertain who will start at forward alongside Hull's Jozy Altidore. Ching and Colorado's Conor Casey have been competing to make the 23-man roster as forwards.
The U.S. team will gather in mid-May ahead of its World Cup opener against England on June 12. The Americans have exhibitions against the Czech Republic (May 25 at East Hartford, Conn.), Turkey (May 29 at Philadelphia) and Australia (June 5 at Roodepoort, South Africa) before meeting England in Rustenburg, South Africa.
