USA national team flyhalf Adam Siddall has taken himself out of the game of rugby for the remainder of 2015.

Siddall has been battling a series of concussions suffered while playing, with the last one being in the USA's game against Romania. While in New Zealand to visit his family, he consulted with doctors, and decided he needed to sit out 2015.

Siddall sent a letter to USA Rugby CEO Nigel Melville and USA Head Coach Mike Tolkin to inform then that he will not be playing at all this year.

The decision, he said, was a disappointing one because it means he will miss the Rugby World Cup, but one he needed to take for his long-term health.