US Open 2013: Laura Robson 'disappointed' by defeat to Li Na

British number one Laura Robson admits it is "disappointing" to exit the US Open, after losing to China's Li Na in the third round at Flushing Meadows.

The 19-year-old was beaten 6-2 7-5 in the first Gland Slam tournament she has been seeded in.

Robson says she has "a lot to work on" to improve her game, but believes she is going "in the right direction".