World champion Tyson Gay fell in the US 200m trials to end his hopes of winning an Olympic sprint double in Beijing.

Gay, who won gold in the 100m and 200m in Japan last year, grabbed at his hamstring after tumbled to the track with severe cramp.

The American policy of only picking the three fastest athletes in the trials means Gay is out of the 200m squad.

Gay, 25, has already qualified for the 100m, recently running a wind-assisted 9.68 seconds to win the US trials.