South African-born Wales flank Andries Pretorius has been forced into retirement by a rare auto-immune condition.

The 29-year-old's club Worcester said he has neuromyotonia (or Isaacs' Syndrome) which causes continuous muscle cramping.

'I can't perform to the standard I know is required to push myself and my team-mates without hurting myself,' he said.

Pretorius made two Test appearances for Wales on their June 2013 tour to Japan.

How Pretorius went from an orange farm in Groblersdal to playing for Wales

Photo: Huw Evans Picture Agency