Former Wales and British and Irish Lions captain Sam Warburton has called for increased player protection.
He said he fears that a professional player could die on the pitch.
The 30-year-old retired last year after winning 79 Test caps and having battled injuries which required surgery to his neck and knee.
In his autobiography, Open Sides, he writes of the safety of the modern game.
Warburton has spent his entire professional career with Cardiff Blues, making his debut for his hometown region in April 2009, and is one of the most successful British & Irish Lions captains of all time.
He bowed out of rugby with a glittering CV including leading Wales to Grand Slam and Six Nations glory as well as to two Rugby World Cups.
He is only the second man to captain the Lions on two tours as he led the famous touring team to New Zealand.