Borland (pictured), a leading rookie last season, reported on Friday that he 'doesn't think it's worth the risk' to continue playing. Head trauma is an issue that has rattled the football league and prompted a massive lawsuit against the NFL. The announcement comes as an unexpected blow to the 49ers, who have already had a difficult off-season and also saw standout linebacker Patrick Willis retire last week. Original Article: http://www.dailymail.co.uk/news/artic... Original Video: http://www.dailymail.co.uk/video/news... Daily Mail Facebook: / dailymail Daily Mail IG: / dailymail Daily Mail Snap: / 8392137033 Daily Mail Twitter: / mailonline Daily Mail Pinterest: http://pinterest.co.uk/dailymail Daily Mail Google+: https://plus.google.com/+DailyMail/posts Get the free Daily Mail mobile app: http://dailymail.co.uk/mobile