BBC Radio Five Live have just stated that it was a back injury that caused the retirement...
The injury apparently occurred when "...he hit shot and started grimacing and twisting. He actually played a good set but it was obvious something was wrong..."
And then Andy .... "..shuffled off court, arm around the physio"
According to people around Andy his "back went into spasms"
and Andy has said that he is "Just going to have to see what it feels like tomorrow morning.."
It's kind of worrying that a 19 year old is having "back spasms"