John Isner pulls out of Cincinnati Open

John Isner has been forced to pull out of the Cincinnati Open with a back injury.

The American was defeated in straight sets by Richard Gasquet in the semi-finals of the Rogers Cup on Saturday.

Despite coming through that match, the world number 11 has now ruled himself out of the warm-up tournament for the US Open. A lucky loser will be named as Isner's replacement.

Rafael Nadal, Jo-Wilfried Tsonga and Fernando Verdasco have also withdrawn from the tournament through injury.